init

.venv/lib/python3.8/site-packages/traitlets/config/__init__.py

@@ -0,0 +1,8 @@
+# encoding: utf-8
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+from .application import *
+from .configurable import *
+from .loader import Config

.venv/lib/python3.8/site-packages/traitlets/config/application.py

@@ -0,0 +1,898 @@
+"""A base class for a configurable application."""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+
+from collections import defaultdict, OrderedDict
+from copy import deepcopy
+import functools
+import json
+import logging
+import os
+import pprint
+import re
+import sys
+import warnings
+
+from traitlets.config.configurable import Configurable, SingletonConfigurable
+from traitlets.config.loader import (
+    KVArgParseConfigLoader, PyFileConfigLoader, Config, ArgumentError, ConfigFileNotFound, JSONFileConfigLoader
+)
+from traitlets.traitlets import (
+    Bool, Unicode, List, Enum, Dict, Instance, TraitError, observe, observe_compat, default,
+)
+
+from ..utils.importstring import import_item
+from ..utils import cast_unicode
+from traitlets.utils.text import indent, wrap_paragraphs
+from textwrap import dedent
+
+
+#-----------------------------------------------------------------------------
+# Descriptions for the various sections
+#-----------------------------------------------------------------------------
+# merge flags&aliases into options
+option_description = """
+The options below are convenience aliases to configurable class-options,
+as listed in the "Equivalent to" description-line of the aliases.
+To see all configurable class-options for some <cmd>, use:
+    <cmd> --help-all
+""".strip()  # trim newlines of front and back
+
+keyvalue_description = """
+The command-line option below sets the respective configurable class-parameter:
+    --Class.parameter=value
+This line is evaluated in Python, so simple expressions are allowed.
+For instance, to set `C.a=[0,1,2]`, you may type this:
+    --C.a='range(3)'
+""".strip() # trim newlines of front and back
+
+# sys.argv can be missing, for example when python is embedded. See the docs
+# for details: http://docs.python.org/2/c-api/intro.html#embedding-python
+if not hasattr(sys, "argv"):
+    sys.argv = [""]
+
+subcommand_description = """
+Subcommands are launched as `{app} cmd [args]`. For information on using
+subcommand 'cmd', do: `{app} cmd -h`.
+"""
+# get running program name
+
+#-----------------------------------------------------------------------------
+# Application class
+#-----------------------------------------------------------------------------
+
+
+
+_envvar = os.environ.get('TRAITLETS_APPLICATION_RAISE_CONFIG_FILE_ERROR','')
+if _envvar.lower() in {'1','true'}:
+    TRAITLETS_APPLICATION_RAISE_CONFIG_FILE_ERROR = True
+elif _envvar.lower() in {'0','false',''} :
+    TRAITLETS_APPLICATION_RAISE_CONFIG_FILE_ERROR = False
+else:
+    raise ValueError("Unsupported value for environment variable: 'TRAITLETS_APPLICATION_RAISE_CONFIG_FILE_ERROR' is set to '%s' which is none of  {'0', '1', 'false', 'true', ''}."% _envvar )
+
+
+def catch_config_error(method):
+    """Method decorator for catching invalid config (Trait/ArgumentErrors) during init.
+
+    On a TraitError (generally caused by bad config), this will print the trait's
+    message, and exit the app.
+
+    For use on init methods, to prevent invoking excepthook on invalid input.
+    """
+    @functools.wraps(method)
+    def inner(app, *args, **kwargs):
+        try:
+            return method(app, *args, **kwargs)
+        except (TraitError, ArgumentError) as e:
+            app.log.fatal("Bad config encountered during initialization: %s", e)
+            app.log.debug("Config at the time: %s", app.config)
+            app.exit(1)
+
+    return inner
+
+class ApplicationError(Exception):
+    pass
+
+
+class LevelFormatter(logging.Formatter):
+    """Formatter with additional `highlevel` record
+
+    This field is empty if log level is less than highlevel_limit,
+    otherwise it is formatted with self.highlevel_format.
+
+    Useful for adding 'WARNING' to warning messages,
+    without adding 'INFO' to info, etc.
+    """
+    highlevel_limit = logging.WARN
+    highlevel_format = " %(levelname)s |"
+
+    def format(self, record):
+        if record.levelno >= self.highlevel_limit:
+            record.highlevel = self.highlevel_format % record.__dict__
+        else:
+            record.highlevel = ""
+        return super(LevelFormatter, self).format(record)
+
+
+class Application(SingletonConfigurable):
+    """A singleton application with full configuration support."""
+
+    # The name of the application, will usually match the name of the command
+    # line application
+    name = Unicode('application')
+
+    # The description of the application that is printed at the beginning
+    # of the help.
+    description = Unicode('This is an application.')
+    # default section descriptions
+    option_description = Unicode(option_description)
+    keyvalue_description = Unicode(keyvalue_description)
+    subcommand_description = Unicode(subcommand_description)
+
+    python_config_loader_class = PyFileConfigLoader
+    json_config_loader_class = JSONFileConfigLoader
+
+    # The usage and example string that goes at the end of the help string.
+    examples = Unicode()
+
+    # A sequence of Configurable subclasses whose config=True attributes will
+    # be exposed at the command line.
+    classes = []
+
+    def _classes_inc_parents(self, classes=None):
+        """Iterate through configurable classes, including configurable parents
+
+        :param classes:
+            The list of classes to iterate; if not set, uses :attr:`classes`.
+
+        Children should always be after parents, and each class should only be
+        yielded once.
+        """
+        if classes is None:
+            classes = self.classes
+
+        seen = set()
+        for c in classes:
+            # We want to sort parents before children, so we reverse the MRO
+            for parent in reversed(c.mro()):
+                if issubclass(parent, Configurable) and (parent not in seen):
+                    seen.add(parent)
+                    yield parent
+
+    # The version string of this application.
+    version = Unicode('0.0')
+
+    # the argv used to initialize the application
+    argv = List()
+
+    # Whether failing to load config files should prevent startup
+    raise_config_file_errors = Bool(TRAITLETS_APPLICATION_RAISE_CONFIG_FILE_ERROR)
+
+    # The log level for the application
+    log_level = Enum((0,10,20,30,40,50,'DEBUG','INFO','WARN','ERROR','CRITICAL'),
+                    default_value=logging.WARN,
+                    help="Set the log level by value or name.").tag(config=True)
+
+    @observe('log_level')
+    @observe_compat
+    def _log_level_changed(self, change):
+        """Adjust the log level when log_level is set."""
+        new = change.new
+        if isinstance(new, str):
+            new = getattr(logging, new)
+            self.log_level = new
+        self.log.setLevel(new)
+
+    _log_formatter_cls = LevelFormatter
+
+    log_datefmt = Unicode("%Y-%m-%d %H:%M:%S",
+        help="The date format used by logging formatters for %(asctime)s"
+    ).tag(config=True)
+
+    log_format = Unicode("[%(name)s]%(highlevel)s %(message)s",
+        help="The Logging format template",
+    ).tag(config=True)
+
+    @observe('log_datefmt', 'log_format')
+    @observe_compat
+    def _log_format_changed(self, change):
+        """Change the log formatter when log_format is set."""
+        _log_handler = self._get_log_handler()
+        if not _log_handler:
+            warnings.warn(
+                f"No Handler found on {self.log}, setting log_format will have no effect",
+                RuntimeWarning,
+            )
+            return
+        _log_formatter = self._log_formatter_cls(fmt=self.log_format, datefmt=self.log_datefmt)
+        _log_handler.setFormatter(_log_formatter)
+
+    @default('log')
+    def _log_default(self):
+        """Start logging for this application.
+
+        The default is to log to stderr using a StreamHandler, if no default
+        handler already exists.  The log level starts at logging.WARN, but this
+        can be adjusted by setting the ``log_level`` attribute.
+        """
+        log = logging.getLogger(self.__class__.__name__)
+        log.setLevel(self.log_level)
+        log.propagate = False
+        _log = log # copied from Logger.hasHandlers() (new in Python 3.2)
+        while _log:
+            if _log.handlers:
+                return log
+            if not _log.propagate:
+                break
+            else:
+                _log = _log.parent
+        if sys.executable and sys.executable.endswith('pythonw.exe'):
+            # this should really go to a file, but file-logging is only
+            # hooked up in parallel applications
+            _log_handler = logging.StreamHandler(open(os.devnull, 'w'))
+        else:
+            _log_handler = logging.StreamHandler()
+        _log_formatter = self._log_formatter_cls(fmt=self.log_format, datefmt=self.log_datefmt)
+        _log_handler.setFormatter(_log_formatter)
+        log.addHandler(_log_handler)
+        return log
+
+    #: the alias map for configurables
+    #: Keys might strings or tuples for additional options; single-letter alias accessed like `-v`.
+    #: Values might be like "Class.trait" strings of two-tuples: (Class.trait, help-text).
+    aliases = {'log-level' : 'Application.log_level'}
+
+    # flags for loading Configurables or store_const style flags
+    # flags are loaded from this dict by '--key' flags
+    # this must be a dict of two-tuples, the first element being the Config/dict
+    # and the second being the help string for the flag
+    flags = {
+        'debug': ({
+            'Application': {
+                'log_level': logging.DEBUG,
+            },
+        }, "Set log-level to debug, for the most verbose logging."),
+        'show-config': ({
+            'Application': {
+                'show_config': True,
+            },
+        }, "Show the application's configuration (human-readable format)"),
+        'show-config-json': ({
+            'Application': {
+                'show_config_json': True,
+            },
+        }, "Show the application's configuration (json format)"),
+    }
+
+    # subcommands for launching other applications
+    # if this is not empty, this will be a parent Application
+    # this must be a dict of two-tuples,
+    # the first element being the application class/import string
+    # and the second being the help string for the subcommand
+    subcommands = Dict()
+    # parse_command_line will initialize a subapp, if requested
+    subapp = Instance('traitlets.config.application.Application', allow_none=True)
+
+    # extra command-line arguments that don't set config values
+    extra_args = List(Unicode())
+
+    cli_config = Instance(Config, (), {},
+        help="""The subset of our configuration that came from the command-line
+
+        We re-load this configuration after loading config files,
+        to ensure that it maintains highest priority.
+        """
+    )
+
+    _loaded_config_files = List()
+
+    show_config = Bool(
+        help="Instead of starting the Application, dump configuration to stdout"
+    ).tag(config=True)
+
+    show_config_json = Bool(
+        help="Instead of starting the Application, dump configuration to stdout (as JSON)"
+    ).tag(config=True)
+
+    @observe('show_config_json')
+    def _show_config_json_changed(self, change):
+        self.show_config = change.new
+
+    @observe('show_config')
+    def _show_config_changed(self, change):
+        if change.new:
+            self._save_start = self.start
+            self.start = self.start_show_config
+
+    def __init__(self, **kwargs):
+        SingletonConfigurable.__init__(self, **kwargs)
+        # Ensure my class is in self.classes, so my attributes appear in command line
+        # options and config files.
+        cls = self.__class__
+        if cls not in self.classes:
+            if self.classes is cls.classes:
+                # class attr, assign instead of insert
+                self.classes = [cls] + self.classes
+            else:
+                self.classes.insert(0, self.__class__)
+
+    @observe('config')
+    @observe_compat
+    def _config_changed(self, change):
+        super(Application, self)._config_changed(change)
+        self.log.debug('Config changed: %r', change.new)
+
+    @catch_config_error
+    def initialize(self, argv=None):
+        """Do the basic steps to configure me.
+
+        Override in subclasses.
+        """
+        self.parse_command_line(argv)
+
+
+    def start(self):
+        """Start the app mainloop.
+
+        Override in subclasses.
+        """
+        if self.subapp is not None:
+            return self.subapp.start()
+
+    def start_show_config(self):
+        """start function used when show_config is True"""
+        config = self.config.copy()
+        # exclude show_config flags from displayed config
+        for cls in self.__class__.mro():
+            if cls.__name__ in config:
+                cls_config = config[cls.__name__]
+                cls_config.pop('show_config', None)
+                cls_config.pop('show_config_json', None)
+
+        if self.show_config_json:
+            json.dump(config, sys.stdout,
+                      indent=1, sort_keys=True, default=repr)
+            # add trailing newline
+            sys.stdout.write('\n')
+            return
+
+        if self._loaded_config_files:
+            print("Loaded config files:")
+            for f in self._loaded_config_files:
+                print('  ' + f)
+            print()
+
+        for classname in sorted(config):
+            class_config = config[classname]
+            if not class_config:
+                continue
+            print(classname)
+            pformat_kwargs = dict(indent=4, compact=True)
+
+            for traitname in sorted(class_config):
+                value = class_config[traitname]
+                print('  .{} = {}'.format(
+                    traitname,
+                    pprint.pformat(value, **pformat_kwargs),
+                ))
+
+    def print_alias_help(self):
+        """Print the alias parts of the help."""
+        print('\n'.join(self.emit_alias_help()))
+
+    def emit_alias_help(self):
+        """Yield the lines for alias part of the help."""
+        if not self.aliases:
+            return
+
+        classdict = {}
+        for cls in self.classes:
+            # include all parents (up to, but excluding Configurable) in available names
+            for c in cls.mro()[:-3]:
+                classdict[c.__name__] = c
+
+        for alias, longname in self.aliases.items():
+            try:
+                if isinstance(longname, tuple):
+                    longname, fhelp = longname
+                else:
+                    fhelp = None
+                classname, traitname = longname.split('.')[-2:]
+                longname = classname + '.' + traitname
+                cls = classdict[classname]
+
+                trait = cls.class_traits(config=True)[traitname]
+                fhelp = cls.class_get_trait_help(trait, helptext=fhelp).splitlines()
+
+                if not isinstance(alias, tuple):
+                    alias = (alias, )
+                alias = sorted(alias, key=len)
+                alias = ', '.join(('--%s' if len(m) > 1 else '-%s') % m
+                                  for m in alias)
+
+                # reformat first line
+                fhelp[0] = fhelp[0].replace('--' + longname, alias)
+                for l in fhelp:
+                    yield l
+                yield indent("Equivalent to: [--%s]" % longname)
+            except Exception as ex:
+                self.log.error('Failed collecting help-message for alias %r, due to: %s',
+                               alias, ex)
+                raise
+
+    def print_flag_help(self):
+        """Print the flag part of the help."""
+        print('\n'.join(self.emit_flag_help()))
+
+    def emit_flag_help(self):
+        """Yield the lines for the flag part of the help."""
+        if not self.flags:
+            return
+
+        for flags, (cfg, fhelp) in self.flags.items():
+            try:
+                if not isinstance(flags, tuple):
+                    flags = (flags, )
+                flags = sorted(flags, key=len)
+                flags = ', '.join(('--%s' if len(m) > 1 else '-%s') % m
+                                  for m in flags)
+                yield flags
+                yield indent(dedent(fhelp.strip()))
+                cfg_list = ' '.join('--%s.%s=%s' %(clname, prop, val)
+                                    for clname, props_dict
+                                    in cfg.items()
+                                    for prop, val in props_dict.items())
+                cfg_txt = "Equivalent to: [%s]" % cfg_list
+                yield indent(dedent(cfg_txt))
+            except Exception as ex:
+                self.log.error('Failed collecting help-message for flag %r, due to: %s',
+                               flags, ex)
+                raise
+
+    def print_options(self):
+        """Print the options part of the help."""
+        print('\n'.join(self.emit_options_help()))
+
+    def emit_options_help(self):
+        """Yield the lines for the options part of the help."""
+        if not self.flags and not self.aliases:
+            return
+        header = 'Options'
+        yield header
+        yield '=' * len(header)
+        for p in wrap_paragraphs(self.option_description):
+            yield p
+            yield ''
+
+        for l in self.emit_flag_help():
+            yield l
+        for l in self.emit_alias_help():
+            yield l
+        yield ''
+
+    def print_subcommands(self):
+        """Print the subcommand part of the help."""
+        print('\n'.join(self.emit_subcommands_help()))
+
+    def emit_subcommands_help(self):
+        """Yield the lines for the subcommand part of the help."""
+        if not self.subcommands:
+            return
+
+        header = "Subcommands"
+        yield header
+        yield '=' * len(header)
+        for p in wrap_paragraphs(self.subcommand_description.format(
+                    app=self.name)):
+            yield p
+            yield ''
+        for subc, (cls, help) in self.subcommands.items():
+            yield subc
+            if help:
+                yield indent(dedent(help.strip()))
+        yield ''
+
+    def emit_help_epilogue(self, classes):
+        """Yield the very bottom lines of the help message.
+
+        If classes=False (the default), print `--help-all` msg.
+        """
+        if not classes:
+            yield "To see all available configurables, use `--help-all`."
+            yield ''
+
+    def print_help(self, classes=False):
+        """Print the help for each Configurable class in self.classes.
+
+        If classes=False (the default), only flags and aliases are printed.
+        """
+        print('\n'.join(self.emit_help(classes=classes)))
+
+    def emit_help(self, classes=False):
+        """Yield the help-lines for each Configurable class in self.classes.
+
+        If classes=False (the default), only flags and aliases are printed.
+        """
+        for l in self.emit_description():
+            yield l
+        for l in self.emit_subcommands_help():
+            yield l
+        for l in self.emit_options_help():
+            yield l
+
+        if classes:
+            help_classes = self._classes_with_config_traits()
+            if help_classes:
+                yield "Class options"
+                yield "============="
+                for p in wrap_paragraphs(self.keyvalue_description):
+                    yield p
+                    yield ''
+
+            for cls in help_classes:
+                yield cls.class_get_help()
+                yield ''
+        for l in self.emit_examples():
+            yield l
+
+        for l in self.emit_help_epilogue(classes):
+            yield l
+
+    def document_config_options(self):
+        """Generate rST format documentation for the config options this application
+
+        Returns a multiline string.
+        """
+        return '\n'.join(c.class_config_rst_doc()
+                         for c in self._classes_inc_parents())
+
+    def print_description(self):
+        """Print the application description."""
+        print('\n'.join(self.emit_description()))
+
+    def emit_description(self):
+        """Yield lines with the application description."""
+        for p in wrap_paragraphs(self.description or self.__doc__):
+            yield p
+            yield ''
+
+    def print_examples(self):
+        """Print usage and examples (see `emit_examples()`). """
+        print('\n'.join(self.emit_examples()))
+
+    def emit_examples(self):
+        """Yield lines with the usage and examples.
+
+        This usage string goes at the end of the command line help string
+        and should contain examples of the application's usage.
+        """
+        if self.examples:
+            yield "Examples"
+            yield "--------"
+            yield ''
+            yield indent(dedent(self.examples.strip()))
+            yield ''
+
+    def print_version(self):
+        """Print the version string."""
+        print(self.version)
+
+    @catch_config_error
+    def initialize_subcommand(self, subc, argv=None):
+        """Initialize a subcommand with argv."""
+        subapp, _ = self.subcommands.get(subc)
+
+        if isinstance(subapp, str):
+            subapp = import_item(subapp)
+
+        ## Cannot issubclass() on a non-type (SOhttp://stackoverflow.com/questions/8692430)
+        if isinstance(subapp, type) and issubclass(subapp, Application):
+            # Clear existing instances before...
+            self.__class__.clear_instance()
+            # instantiating subapp...
+            self.subapp = subapp.instance(parent=self)
+        elif callable(subapp):
+            # or ask factory to create it...
+            self.subapp = subapp(self)
+        else:
+            raise AssertionError("Invalid mappings for subcommand '%s'!" % subc)
+
+        # ... and finally initialize subapp.
+        self.subapp.initialize(argv)
+
+    def flatten_flags(self):
+        """Flatten flags and aliases for loaders, so cl-args override as expected.
+
+        This prevents issues such as an alias pointing to InteractiveShell,
+        but a config file setting the same trait in TerminalInteraciveShell
+        getting inappropriate priority over the command-line arg.
+        Also, loaders expect ``(key: longname)`` and not ````key: (longname, help)`` items.
+
+        Only aliases with exactly one descendent in the class list
+        will be promoted.
+
+        """
+        # build a tree of classes in our list that inherit from a particular
+        # it will be a dict by parent classname of classes in our list
+        # that are descendents
+        mro_tree = defaultdict(list)
+        for cls in self.classes:
+            clsname = cls.__name__
+            for parent in cls.mro()[1:-3]:
+                # exclude cls itself and Configurable,HasTraits,object
+                mro_tree[parent.__name__].append(clsname)
+        # flatten aliases, which have the form:
+        # { 'alias' : 'Class.trait' }
+        aliases = {}
+        for alias, longname in self.aliases.items():
+            if isinstance(longname, tuple):
+                longname, _ = longname
+            cls, trait = longname.split('.', 1)
+            children = mro_tree[cls]
+            if len(children) == 1:
+                # exactly one descendent, promote alias
+                cls = children[0]
+            if not isinstance(aliases, tuple):
+                alias = (alias, )
+            for al in alias:
+                aliases[al] = '.'.join([cls,trait])
+
+        # flatten flags, which are of the form:
+        # { 'key' : ({'Cls' : {'trait' : value}}, 'help')}
+        flags = {}
+        for key, (flagdict, help) in self.flags.items():
+            newflag = {}
+            for cls, subdict in flagdict.items():
+                children = mro_tree[cls]
+                # exactly one descendent, promote flag section
+                if len(children) == 1:
+                    cls = children[0]
+
+                if cls in newflag:
+                    newflag[cls].update(subdict)
+                else:
+                    newflag[cls] = subdict
+
+            if not isinstance(key, tuple):
+                key = (key, )
+            for k in key:
+                flags[k] = (newflag, help)
+        return flags, aliases
+
+    def _create_loader(self, argv, aliases, flags, classes):
+        return KVArgParseConfigLoader(argv, aliases, flags, classes=classes,
+                                      log=self.log)
+
+    @catch_config_error
+    def parse_command_line(self, argv=None):
+        """Parse the command line arguments."""
+        assert not isinstance(argv, str)
+        argv = sys.argv[1:] if argv is None else argv
+        self.argv = [cast_unicode(arg) for arg in argv ]
+
+        if argv and argv[0] == 'help':
+            # turn `ipython help notebook` into `ipython notebook -h`
+            argv = argv[1:] + ['-h']
+
+        if self.subcommands and len(argv) > 0:
+            # we have subcommands, and one may have been specified
+            subc, subargv = argv[0], argv[1:]
+            if re.match(r'^\w(\-?\w)*$', subc) and subc in self.subcommands:
+                # it's a subcommand, and *not* a flag or class parameter
+                return self.initialize_subcommand(subc, subargv)
+
+        # Arguments after a '--' argument are for the script IPython may be
+        # about to run, not IPython iteslf. For arguments parsed here (help and
+        # version), we want to only search the arguments up to the first
+        # occurrence of '--', which we're calling interpreted_argv.
+        try:
+            interpreted_argv = argv[:argv.index('--')]
+        except ValueError:
+            interpreted_argv = argv
+
+        if any(x in interpreted_argv for x in ('-h', '--help-all', '--help')):
+            self.print_help('--help-all' in interpreted_argv)
+            self.exit(0)
+
+        if '--version' in interpreted_argv or '-V' in interpreted_argv:
+            self.print_version()
+            self.exit(0)
+
+        # flatten flags&aliases, so cl-args get appropriate priority:
+        flags, aliases = self.flatten_flags()
+        classes = tuple(self._classes_with_config_traits())
+        loader = self._create_loader(argv, aliases, flags, classes=classes)
+        try:
+            self.cli_config = deepcopy(loader.load_config())
+        except SystemExit:
+            # traitlets 5: no longer print help output on error
+            # help output is huge, and comes after the error
+            raise
+        self.update_config(self.cli_config)
+        # store unparsed args in extra_args
+        self.extra_args = loader.extra_args
+
+    @classmethod
+    def _load_config_files(cls, basefilename, path=None, log=None, raise_config_file_errors=False):
+        """Load config files (py,json) by filename and path.
+
+        yield each config object in turn.
+        """
+
+        if not isinstance(path, list):
+            path = [path]
+        for path in path[::-1]:
+            # path list is in descending priority order, so load files backwards:
+            pyloader = cls.python_config_loader_class(basefilename+'.py', path=path, log=log)
+            if log:
+                log.debug("Looking for %s in %s", basefilename, path or os.getcwd())
+            jsonloader = cls.json_config_loader_class(basefilename+'.json', path=path, log=log)
+            loaded = []
+            filenames = []
+            for loader in [pyloader, jsonloader]:
+                config = None
+                try:
+                    config = loader.load_config()
+                except ConfigFileNotFound:
+                    pass
+                except Exception:
+                    # try to get the full filename, but it will be empty in the
+                    # unlikely event that the error raised before filefind finished
+                    filename = loader.full_filename or basefilename
+                    # problem while running the file
+                    if raise_config_file_errors:
+                        raise
+                    if log:
+                        log.error("Exception while loading config file %s",
+                                filename, exc_info=True)
+                else:
+                    if log:
+                        log.debug("Loaded config file: %s", loader.full_filename)
+                if config:
+                    for filename, earlier_config in zip(filenames, loaded):
+                        collisions = earlier_config.collisions(config)
+                        if collisions and log:
+                            log.warning("Collisions detected in {0} and {1} config files."
+                                " {1} has higher priority: {2}".format(
+                                filename, loader.full_filename, json.dumps(collisions, indent=2),
+                            ))
+                    yield (config, loader.full_filename)
+                    loaded.append(config)
+                    filenames.append(loader.full_filename)
+
+    @property
+    def loaded_config_files(self):
+        """Currently loaded configuration files"""
+        return self._loaded_config_files[:]
+
+    @catch_config_error
+    def load_config_file(self, filename, path=None):
+        """Load config files by filename and path."""
+        filename, ext = os.path.splitext(filename)
+        new_config = Config()
+        for (config, filename) in self._load_config_files(filename, path=path, log=self.log,
+            raise_config_file_errors=self.raise_config_file_errors,
+        ):
+            new_config.merge(config)
+            if filename not in self._loaded_config_files:  # only add to list of loaded files if not previously loaded
+                self._loaded_config_files.append(filename)
+        # add self.cli_config to preserve CLI config priority
+        new_config.merge(self.cli_config)
+        self.update_config(new_config)
+
+    def _classes_with_config_traits(self, classes=None):
+        """
+        Yields only classes with configurable traits, and their subclasses.
+
+        :param classes:
+            The list of classes to iterate; if not set, uses :attr:`classes`.
+
+        Thus, produced sample config-file will contain all classes
+        on which a trait-value may be overridden:
+
+        - either on the class owning the trait,
+        - or on its subclasses, even if those subclasses do not define
+          any traits themselves.
+        """
+        if classes is None:
+            classes = self.classes
+
+        cls_to_config = OrderedDict( (cls, bool(cls.class_own_traits(config=True)))
+                              for cls
+                              in self._classes_inc_parents(classes))
+
+        def is_any_parent_included(cls):
+            return any(b in cls_to_config and cls_to_config[b] for b in cls.__bases__)
+
+        ## Mark "empty" classes for inclusion if their parents own-traits,
+        #  and loop until no more classes gets marked.
+        #
+        while True:
+            to_incl_orig = cls_to_config.copy()
+            cls_to_config = OrderedDict( (cls, inc_yes or is_any_parent_included(cls))
+                                  for cls, inc_yes
+                                  in cls_to_config.items())
+            if cls_to_config == to_incl_orig:
+                break
+        for cl, inc_yes in cls_to_config.items():
+            if inc_yes:
+                yield cl
+
+    def generate_config_file(self, classes=None):
+        """generate default config file from Configurables"""
+        lines = ["# Configuration file for %s." % self.name]
+        lines.append('')
+        classes = self.classes if classes is None else classes
+        config_classes = list(self._classes_with_config_traits(classes))
+        for cls in config_classes:
+            lines.append(cls.class_config_section(config_classes))
+        return '\n'.join(lines)
+
+    def exit(self, exit_status=0):
+        self.log.debug("Exiting application: %s" % self.name)
+        sys.exit(exit_status)
+
+    @classmethod
+    def launch_instance(cls, argv=None, **kwargs):
+        """Launch a global instance of this Application
+
+        If a global instance already exists, this reinitializes and starts it
+        """
+        app = cls.instance(**kwargs)
+        app.initialize(argv)
+        app.start()
+
+#-----------------------------------------------------------------------------
+# utility functions, for convenience
+#-----------------------------------------------------------------------------
+
+default_aliases = Application.aliases
+default_flags = Application.flags
+
+def boolean_flag(name, configurable, set_help='', unset_help=''):
+    """Helper for building basic --trait, --no-trait flags.
+
+    Parameters
+    ----------
+    name : str
+        The name of the flag.
+    configurable : str
+        The 'Class.trait' string of the trait to be set/unset with the flag
+    set_help : unicode
+        help string for --name flag
+    unset_help : unicode
+        help string for --no-name flag
+
+    Returns
+    -------
+    cfg : dict
+        A dict with two keys: 'name', and 'no-name', for setting and unsetting
+        the trait, respectively.
+    """
+    # default helpstrings
+    set_help = set_help or "set %s=True"%configurable
+    unset_help = unset_help or "set %s=False"%configurable
+
+    cls,trait = configurable.split('.')
+
+    setter = {cls : {trait : True}}
+    unsetter = {cls : {trait : False}}
+    return {name : (setter, set_help), 'no-'+name : (unsetter, unset_help)}
+
+
+def get_config():
+    """Get the config object for the global Application instance, if there is one
+
+    otherwise return an empty config object
+    """
+    if Application.initialized():
+        return Application.instance().config
+    else:
+        return Config()
+
+
+if __name__ == '__main__':
+    Application.launch_instance()

.venv/lib/python3.8/site-packages/traitlets/config/configurable.py

@@ -0,0 +1,560 @@
+"""A base class for objects that are configurable."""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+
+from copy import deepcopy
+import logging
+import warnings
+
+from .loader import Config, LazyConfigValue, DeferredConfig, _is_section_key
+from traitlets.traitlets import (
+    Any,
+    HasTraits,
+    Instance,
+    Container,
+    Dict,
+    observe,
+    observe_compat,
+    default,
+    validate,
+)
+from traitlets.utils.text import indent, wrap_paragraphs
+from textwrap import dedent
+
+
+
+
+#-----------------------------------------------------------------------------
+# Helper classes for Configurables
+#-----------------------------------------------------------------------------
+
+
+class ConfigurableError(Exception):
+    pass
+
+
+class MultipleInstanceError(ConfigurableError):
+    pass
+
+#-----------------------------------------------------------------------------
+# Configurable implementation
+#-----------------------------------------------------------------------------
+
+class Configurable(HasTraits):
+
+    config = Instance(Config, (), {})
+    parent = Instance('traitlets.config.configurable.Configurable', allow_none=True)
+
+    def __init__(self, **kwargs):
+        """Create a configurable given a config config.
+
+        Parameters
+        ----------
+        config : Config
+            If this is empty, default values are used. If config is a
+            :class:`Config` instance, it will be used to configure the
+            instance.
+        parent : Configurable instance, optional
+            The parent Configurable instance of this object.
+
+        Notes
+        -----
+        Subclasses of Configurable must call the :meth:`__init__` method of
+        :class:`Configurable` *before* doing anything else and using
+        :func:`super`::
+
+            class MyConfigurable(Configurable):
+                def __init__(self, config=None):
+                    super(MyConfigurable, self).__init__(config=config)
+                    # Then any other code you need to finish initialization.
+
+        This ensures that instances will be configured properly.
+        """
+        parent = kwargs.pop('parent', None)
+        if parent is not None:
+            # config is implied from parent
+            if kwargs.get('config', None) is None:
+                kwargs['config'] = parent.config
+            self.parent = parent
+
+        config = kwargs.pop('config', None)
+
+        # load kwarg traits, other than config
+        super(Configurable, self).__init__(**kwargs)
+
+        # record traits set by config
+        config_override_names = set()
+        def notice_config_override(change):
+            """Record traits set by both config and kwargs.
+
+            They will need to be overridden again after loading config.
+            """
+            if change.name in kwargs:
+                config_override_names.add(change.name)
+        self.observe(notice_config_override)
+
+        # load config
+        if config is not None:
+            # We used to deepcopy, but for now we are trying to just save
+            # by reference.  This *could* have side effects as all components
+            # will share config. In fact, I did find such a side effect in
+            # _config_changed below. If a config attribute value was a mutable type
+            # all instances of a component were getting the same copy, effectively
+            # making that a class attribute.
+            # self.config = deepcopy(config)
+            self.config = config
+        else:
+            # allow _config_default to return something
+            self._load_config(self.config)
+        self.unobserve(notice_config_override)
+
+        for name in config_override_names:
+            setattr(self, name, kwargs[name])
+
+
+    #-------------------------------------------------------------------------
+    # Static trait notifiations
+    #-------------------------------------------------------------------------
+
+    @classmethod
+    def section_names(cls):
+        """return section names as a list"""
+        return  [c.__name__ for c in reversed(cls.__mro__) if
+            issubclass(c, Configurable) and issubclass(cls, c)
+        ]
+
+    def _find_my_config(self, cfg):
+        """extract my config from a global Config object
+
+        will construct a Config object of only the config values that apply to me
+        based on my mro(), as well as those of my parent(s) if they exist.
+
+        If I am Bar and my parent is Foo, and their parent is Tim,
+        this will return merge following config sections, in this order::
+
+            [Bar, Foo.Bar, Tim.Foo.Bar]
+
+        With the last item being the highest priority.
+        """
+        cfgs = [cfg]
+        if self.parent:
+            cfgs.append(self.parent._find_my_config(cfg))
+        my_config = Config()
+        for c in cfgs:
+            for sname in self.section_names():
+                # Don't do a blind getattr as that would cause the config to
+                # dynamically create the section with name Class.__name__.
+                if c._has_section(sname):
+                    my_config.merge(c[sname])
+        return my_config
+
+    def _load_config(self, cfg, section_names=None, traits=None):
+        """load traits from a Config object"""
+
+        if traits is None:
+            traits = self.traits(config=True)
+        if section_names is None:
+            section_names = self.section_names()
+
+        my_config = self._find_my_config(cfg)
+
+        # hold trait notifications until after all config has been loaded
+        with self.hold_trait_notifications():
+            for name, config_value in my_config.items():
+                if name in traits:
+                    if isinstance(config_value, LazyConfigValue):
+                        # ConfigValue is a wrapper for using append / update on containers
+                        # without having to copy the initial value
+                        initial = getattr(self, name)
+                        config_value = config_value.get_value(initial)
+                    elif isinstance(config_value, DeferredConfig):
+                        # DeferredConfig tends to come from CLI/environment variables
+                        config_value = config_value.get_value(traits[name])
+                    # We have to do a deepcopy here if we don't deepcopy the entire
+                    # config object. If we don't, a mutable config_value will be
+                    # shared by all instances, effectively making it a class attribute.
+                    setattr(self, name, deepcopy(config_value))
+                elif not _is_section_key(name) and not isinstance(config_value, Config):
+                    from difflib import get_close_matches
+                    if isinstance(self, LoggingConfigurable):
+                        warn = self.log.warning
+                    else:
+                        warn = lambda msg: warnings.warn(msg, stacklevel=9)
+                    matches = get_close_matches(name, traits)
+                    msg = "Config option `{option}` not recognized by `{klass}`.".format(
+                        option=name, klass=self.__class__.__name__)
+
+                    if len(matches) == 1:
+                        msg += "  Did you mean `{matches}`?".format(matches=matches[0])
+                    elif len(matches) >= 1:
+                        msg +="  Did you mean one of: `{matches}`?".format(matches=', '.join(sorted(matches)))
+                    warn(msg)
+
+    @observe('config')
+    @observe_compat
+    def _config_changed(self, change):
+        """Update all the class traits having ``config=True`` in metadata.
+
+        For any class trait with a ``config`` metadata attribute that is
+        ``True``, we update the trait with the value of the corresponding
+        config entry.
+        """
+        # Get all traits with a config metadata entry that is True
+        traits = self.traits(config=True)
+
+        # We auto-load config section for this class as well as any parent
+        # classes that are Configurable subclasses.  This starts with Configurable
+        # and works down the mro loading the config for each section.
+        section_names = self.section_names()
+        self._load_config(change.new, traits=traits, section_names=section_names)
+
+    def update_config(self, config):
+        """Update config and load the new values"""
+        # traitlets prior to 4.2 created a copy of self.config in order to trigger change events.
+        # Some projects (IPython < 5) relied upon one side effect of this,
+        # that self.config prior to update_config was not modified in-place.
+        # For backward-compatibility, we must ensure that self.config
+        # is a new object and not modified in-place,
+        # but config consumers should not rely on this behavior.
+        self.config = deepcopy(self.config)
+        # load config
+        self._load_config(config)
+        # merge it into self.config
+        self.config.merge(config)
+        # TODO: trigger change event if/when dict-update change events take place
+        # DO NOT trigger full trait-change
+
+    @classmethod
+    def class_get_help(cls, inst=None):
+        """Get the help string for this class in ReST format.
+
+        If `inst` is given, it's current trait values will be used in place of
+        class defaults.
+        """
+        assert inst is None or isinstance(inst, cls)
+        final_help = []
+        base_classes = ', '.join(p.__name__ for p in cls.__bases__)
+        final_help.append('%s(%s) options' % (cls.__name__, base_classes))
+        final_help.append(len(final_help[0])*'-')
+        for k, v in sorted(cls.class_traits(config=True).items()):
+            help = cls.class_get_trait_help(v, inst)
+            final_help.append(help)
+        return '\n'.join(final_help)
+
+    @classmethod
+    def class_get_trait_help(cls, trait, inst=None, helptext=None):
+        """Get the helptext string for a single trait.
+
+        :param inst:
+            If given, it's current trait values will be used in place of
+            the class default.
+        :param helptext:
+            If not given, uses the `help` attribute of the current trait.
+        """
+        assert inst is None or isinstance(inst, cls)
+        lines = []
+        header = "--%s.%s" % (cls.__name__, trait.name)
+        if isinstance(trait, (Container, Dict)):
+            multiplicity = trait.metadata.get('multiplicity', 'append')
+            if isinstance(trait, Dict):
+                sample_value = '<key-1>=<value-1>'
+            else:
+                sample_value = '<%s-item-1>' % trait.__class__.__name__.lower()
+            if multiplicity == 'append':
+                header = "%s=%s..." % (header, sample_value)
+            else:
+                header = "%s %s..." % (header, sample_value)
+        else:
+            header = '%s=<%s>' % (header, trait.__class__.__name__)
+        #header = "--%s.%s=<%s>" % (cls.__name__, trait.name, trait.__class__.__name__)
+        lines.append(header)
+
+        if helptext is None:
+            helptext = trait.help
+        if helptext != '':
+            helptext = '\n'.join(wrap_paragraphs(helptext, 76))
+            lines.append(indent(helptext))
+
+        if 'Enum' in trait.__class__.__name__:
+            # include Enum choices
+            lines.append(indent('Choices: %s' % trait.info()))
+
+        if inst is not None:
+            lines.append(indent("Current: %r" % (getattr(inst, trait.name),)))
+        else:
+            try:
+                dvr = trait.default_value_repr()
+            except Exception:
+                dvr = None # ignore defaults we can't construct
+            if dvr is not None:
+                if len(dvr) > 64:
+                    dvr = dvr[:61] + "..."
+                lines.append(indent("Default: %s" % dvr))
+
+        return '\n'.join(lines)
+
+    @classmethod
+    def class_print_help(cls, inst=None):
+        """Get the help string for a single trait and print it."""
+        print(cls.class_get_help(inst))
+
+    @classmethod
+    def _defining_class(cls, trait, classes):
+        """Get the class that defines a trait
+
+        For reducing redundant help output in config files.
+        Returns the current class if:
+        - the trait is defined on this class, or
+        - the class where it is defined would not be in the config file
+
+        Parameters
+        ----------
+        trait : Trait
+            The trait to look for
+        classes : list
+            The list of other classes to consider for redundancy.
+            Will return `cls` even if it is not defined on `cls`
+            if the defining class is not in `classes`.
+        """
+        defining_cls = cls
+        for parent in cls.mro():
+            if issubclass(parent, Configurable) and \
+            parent in classes and \
+            parent.class_own_traits(config=True).get(trait.name, None) is trait:
+                defining_cls = parent
+        return defining_cls
+
+    @classmethod
+    def class_config_section(cls, classes=None):
+        """Get the config section for this class.
+
+        Parameters
+        ----------
+        classes : list, optional
+            The list of other classes in the config file.
+            Used to reduce redundant information.
+        """
+        def c(s):
+            """return a commented, wrapped block."""
+            s = '\n\n'.join(wrap_paragraphs(s, 78))
+
+            return '## ' + s.replace('\n', '\n#  ')
+
+        # section header
+        breaker = '#' + '-' * 78
+        parent_classes = ', '.join(
+            p.__name__ for p in cls.__bases__
+            if issubclass(p, Configurable)
+        )
+
+        s = "# %s(%s) configuration" % (cls.__name__, parent_classes)
+        lines = [breaker, s, breaker]
+        # get the description trait
+        desc = cls.class_traits().get('description')
+        if desc:
+            desc = desc.default_value
+        if not desc:
+            # no description from trait, use __doc__
+            desc = getattr(cls, '__doc__', '')
+        if desc:
+            lines.append(c(desc))
+            lines.append('')
+
+        for name, trait in sorted(cls.class_traits(config=True).items()):
+            default_repr = trait.default_value_repr()
+
+            if classes:
+                defining_class = cls._defining_class(trait, classes)
+            else:
+                defining_class = cls
+            if defining_class is cls:
+                # cls owns the trait, show full help
+                if trait.help:
+                    lines.append(c(trait.help))
+                if 'Enum' in type(trait).__name__:
+                    # include Enum choices
+                    lines.append('#  Choices: %s' % trait.info())
+                lines.append('#  Default: %s' % default_repr)
+            else:
+                # Trait appears multiple times and isn't defined here.
+                # Truncate help to first line + "See also Original.trait"
+                if trait.help:
+                    lines.append(c(trait.help.split('\n', 1)[0]))
+                lines.append('#  See also: %s.%s' % (defining_class.__name__, name))
+
+            lines.append('# c.%s.%s = %s' % (cls.__name__, name, default_repr))
+            lines.append('')
+        return '\n'.join(lines)
+
+    @classmethod
+    def class_config_rst_doc(cls):
+        """Generate rST documentation for this class' config options.
+
+        Excludes traits defined on parent classes.
+        """
+        lines = []
+        classname = cls.__name__
+        for k, trait in sorted(cls.class_traits(config=True).items()):
+            ttype = trait.__class__.__name__
+
+            termline = classname + '.' + trait.name
+
+            # Choices or type
+            if 'Enum' in ttype:
+                # include Enum choices
+                termline += ' : ' + trait.info_rst()
+            else:
+                termline += ' : ' + ttype
+            lines.append(termline)
+
+            # Default value
+            try:
+                dvr = trait.default_value_repr()
+            except Exception:
+                dvr = None # ignore defaults we can't construct
+            if dvr is not None:
+                if len(dvr) > 64:
+                    dvr = dvr[:61]+'...'
+                # Double up backslashes, so they get to the rendered docs
+                dvr = dvr.replace("\\n", "\\\\n")
+                lines.append(indent("Default: ``%s``" % dvr))
+                lines.append("")
+
+            help = trait.help or 'No description'
+            lines.append(indent(dedent(help)))
+
+            # Blank line
+            lines.append('')
+
+        return '\n'.join(lines)
+
+
+
+class LoggingConfigurable(Configurable):
+    """A parent class for Configurables that log.
+
+    Subclasses have a log trait, and the default behavior
+    is to get the logger from the currently running Application.
+    """
+
+    log = Any(help="Logger or LoggerAdapter instance")
+
+    @validate("log")
+    def _validate_log(self, proposal):
+        if not isinstance(proposal.value, (logging.Logger, logging.LoggerAdapter)):
+            # warn about unsupported type, but be lenient to allow for duck typing
+            warnings.warn(
+                f"{self.__class__.__name__}.log should be a Logger or LoggerAdapter,"
+                f" got {proposal.value}."
+            )
+        return proposal.value
+
+    @default("log")
+    def _log_default(self):
+        if isinstance(self.parent, LoggingConfigurable):
+            return self.parent.log
+        from traitlets import log
+        return log.get_logger()
+
+    def _get_log_handler(self):
+        """Return the default Handler
+
+        Returns None if none can be found
+        """
+        logger = self.log
+        if isinstance(logger, logging.LoggerAdapter):
+            logger = logger.logger
+        if not getattr(logger, "handlers", None):
+            # no handlers attribute or empty handlers list
+            return None
+        return logger.handlers[0]
+
+
+class SingletonConfigurable(LoggingConfigurable):
+    """A configurable that only allows one instance.
+
+    This class is for classes that should only have one instance of itself
+    or *any* subclass. To create and retrieve such a class use the
+    :meth:`SingletonConfigurable.instance` method.
+    """
+
+    _instance = None
+
+    @classmethod
+    def _walk_mro(cls):
+        """Walk the cls.mro() for parent classes that are also singletons
+
+        For use in instance()
+        """
+
+        for subclass in cls.mro():
+            if issubclass(cls, subclass) and \
+                    issubclass(subclass, SingletonConfigurable) and \
+                    subclass != SingletonConfigurable:
+                yield subclass
+
+    @classmethod
+    def clear_instance(cls):
+        """unset _instance for this class and singleton parents.
+        """
+        if not cls.initialized():
+            return
+        for subclass in cls._walk_mro():
+            if isinstance(subclass._instance, cls):
+                # only clear instances that are instances
+                # of the calling class
+                subclass._instance = None
+
+    @classmethod
+    def instance(cls, *args, **kwargs):
+        """Returns a global instance of this class.
+
+        This method create a new instance if none have previously been created
+        and returns a previously created instance is one already exists.
+
+        The arguments and keyword arguments passed to this method are passed
+        on to the :meth:`__init__` method of the class upon instantiation.
+
+        Examples
+        --------
+        Create a singleton class using instance, and retrieve it::
+
+            >>> from traitlets.config.configurable import SingletonConfigurable
+            >>> class Foo(SingletonConfigurable): pass
+            >>> foo = Foo.instance()
+            >>> foo == Foo.instance()
+            True
+
+        Create a subclass that is retrived using the base class instance::
+
+            >>> class Bar(SingletonConfigurable): pass
+            >>> class Bam(Bar): pass
+            >>> bam = Bam.instance()
+            >>> bam == Bar.instance()
+            True
+        """
+        # Create and save the instance
+        if cls._instance is None:
+            inst = cls(*args, **kwargs)
+            # Now make sure that the instance will also be returned by
+            # parent classes' _instance attribute.
+            for subclass in cls._walk_mro():
+                subclass._instance = inst
+
+        if isinstance(cls._instance, cls):
+            return cls._instance
+        else:
+            raise MultipleInstanceError(
+                "An incompatible sibling of '%s' is already instanciated"
+                " as singleton: %s" % (cls.__name__, type(cls._instance).__name__)
+            )
+
+    @classmethod
+    def initialized(cls):
+        """Has an instance been created?"""
+        return hasattr(cls, "_instance") and cls._instance is not None
+
+
+

.venv/lib/python3.8/site-packages/traitlets/config/manager.py

@@ -0,0 +1,84 @@
+"""Manager to read and modify config data in JSON files.
+"""
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+import errno
+import io
+import json
+import os
+
+from traitlets.config import LoggingConfigurable
+from traitlets.traitlets import Unicode
+
+
+def recursive_update(target, new):
+    """Recursively update one dictionary using another.
+
+    None values will delete their keys.
+    """
+    for k, v in new.items():
+        if isinstance(v, dict):
+            if k not in target:
+                target[k] = {}
+            recursive_update(target[k], v)
+            if not target[k]:
+                # Prune empty subdicts
+                del target[k]
+
+        elif v is None:
+            target.pop(k, None)
+
+        else:
+            target[k] = v
+
+
+class BaseJSONConfigManager(LoggingConfigurable):
+    """General JSON config manager
+
+    Deals with persisting/storing config in a json file
+    """
+
+    config_dir = Unicode('.')
+
+    def ensure_config_dir_exists(self):
+        try:
+            os.makedirs(self.config_dir, 0o755)
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise
+
+    def file_name(self, section_name):
+        return os.path.join(self.config_dir, section_name+'.json')
+
+    def get(self, section_name):
+        """Retrieve the config data for the specified section.
+
+        Returns the data as a dictionary, or an empty dictionary if the file
+        doesn't exist.
+        """
+        filename = self.file_name(section_name)
+        if os.path.isfile(filename):
+            with io.open(filename, encoding='utf-8') as f:
+                return json.load(f)
+        else:
+            return {}
+
+    def set(self, section_name, data):
+        """Store the given config data.
+        """
+        filename = self.file_name(section_name)
+        self.ensure_config_dir_exists()
+
+        f = open(filename, 'w', encoding='utf-8')
+        with f:
+            json.dump(data, f, indent=2)
+
+    def update(self, section_name, new_data):
+        """Modify the config section by recursively updating it with new_data.
+
+        Returns the modified config data as a dictionary.
+        """
+        data = self.get(section_name)
+        recursive_update(data, new_data)
+        self.set(section_name, data)
+        return data

.venv/lib/python3.8/site-packages/traitlets/config/sphinxdoc.py

@@ -0,0 +1,161 @@
+"""Machinery for documenting traitlets config options with Sphinx.
+
+This includes:
+
+- A Sphinx extension defining directives and roles for config options.
+- A function to generate an rst file given an Application instance.
+
+To make this documentation, first set this module as an extension in Sphinx's
+conf.py::
+
+    extensions = [
+        # ...
+        'traitlets.config.sphinxdoc',
+    ]
+
+Autogenerate the config documentation by running code like this before
+Sphinx builds::
+
+    from traitlets.config.sphinxdoc import write_doc
+    from myapp import MyApplication
+
+    writedoc('config/options.rst',    # File to write
+             'MyApp config options',  # Title
+             MyApplication()
+            )
+
+The generated rST syntax looks like this::
+
+    .. configtrait:: Application.log_datefmt
+
+        Description goes here.
+
+    Cross reference like this: :configtrait:`Application.log_datefmt`.
+"""
+from traitlets import Undefined
+from traitlets.utils.text import indent
+from collections import defaultdict
+
+from textwrap import indent as _indent, dedent
+
+
+def setup(app):
+    """Registers the Sphinx extension.
+
+    You shouldn't need to call this directly; configure Sphinx to use this
+    module instead.
+    """
+    app.add_object_type('configtrait', 'configtrait', objname='Config option')
+    metadata = {'parallel_read_safe': True, 'parallel_write_safe': True}
+    return metadata
+
+def interesting_default_value(dv):
+    if (dv is None) or (dv is Undefined):
+        return False
+    if isinstance(dv, (str, list, tuple, dict, set)):
+        return bool(dv)
+    return True
+
+def format_aliases(aliases):
+    fmted = []
+    for a in aliases:
+        dashes = '-' if len(a) == 1 else '--'
+        fmted.append('``%s%s``' % (dashes, a))
+    return ', '.join(fmted)
+
+def class_config_rst_doc(cls, trait_aliases):
+    """Generate rST documentation for this class' config options.
+
+    Excludes traits defined on parent classes.
+    """
+    lines = []
+    classname = cls.__name__
+    for k, trait in sorted(cls.class_traits(config=True).items()):
+        ttype = trait.__class__.__name__
+
+        fullname = classname + '.' + trait.name
+        lines += ['.. configtrait:: ' + fullname,
+                  ''
+                 ]
+
+        help = trait.help.rstrip() or "No description"
+        lines.append(indent(dedent(help)) + "\n")
+
+        # Choices or type
+        if 'Enum' in ttype:
+            # include Enum choices
+            lines.append(
+                indent(":options: " + ", ".join("``%r``" % x for x in trait.values))
+            )
+        else:
+            lines.append(indent(":trait type: " + ttype))
+
+        # Default value
+        # Ignore boring default values like None, [] or ''
+        if interesting_default_value(trait.default_value):
+            try:
+                dvr = trait.default_value_repr()
+            except Exception:
+                dvr = None  # ignore defaults we can't construct
+            if dvr is not None:
+                if len(dvr) > 64:
+                    dvr = dvr[:61] + '...'
+                # Double up backslashes, so they get to the rendered docs
+                dvr = dvr.replace("\\n", "\\\\n")
+                lines.append(indent(":default: ``%s``" % dvr))
+
+        # Command line aliases
+        if trait_aliases[fullname]:
+            fmt_aliases = format_aliases(trait_aliases[fullname])
+            lines.append(indent(":CLI option: " + fmt_aliases))
+
+        # Blank line
+        lines.append('')
+
+    return '\n'.join(lines)
+
+def reverse_aliases(app):
+    """Produce a mapping of trait names to lists of command line aliases.
+    """
+    res = defaultdict(list)
+    for alias, trait in app.aliases.items():
+        res[trait].append(alias)
+
+    # Flags also often act as aliases for a boolean trait.
+    # Treat flags which set one trait to True as aliases.
+    for flag, (cfg, _) in app.flags.items():
+        if len(cfg) == 1:
+            classname = list(cfg)[0]
+            cls_cfg = cfg[classname]
+            if len(cls_cfg) == 1:
+                traitname = list(cls_cfg)[0]
+                if cls_cfg[traitname] is True:
+                    res[classname+'.'+traitname].append(flag)
+
+    return res
+
+def write_doc(path, title, app, preamble=None):
+    """Write a rst file documenting config options for a traitlets application.
+
+    Parameters
+    ----------
+    path : str
+        The file to be written
+    title : str
+        The human-readable title of the document
+    app : traitlets.config.Application
+        An instance of the application class to be documented
+    preamble : str
+        Extra text to add just after the title (optional)
+    """
+    trait_aliases = reverse_aliases(app)
+    with open(path, 'w') as f:
+        f.write(title + '\n')
+        f.write(('=' * len(title)) + '\n')
+        f.write('\n')
+        if preamble is not None:
+            f.write(preamble + '\n\n')
+
+        for c in app._classes_inc_parents():
+            f.write(class_config_rst_doc(c, trait_aliases))
+            f.write('\n')

.venv/lib/python3.8/site-packages/traitlets/config/tests/test_application.py

@@ -0,0 +1,767 @@
+# coding: utf-8
+"""
+Tests for traitlets.config.application.Application
+"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import contextlib
+import io
+import json
+import logging
+import os
+import sys
+from io import StringIO
+from tempfile import TemporaryDirectory
+from unittest import TestCase
+
+import pytest
+from pytest import mark
+
+from traitlets import (
+    Bool,
+    Bytes,
+    Dict,
+    HasTraits,
+    Integer,
+    List,
+    Set,
+    Tuple,
+    Unicode,
+)
+from traitlets.config.application import Application
+from traitlets.config.configurable import Configurable
+from traitlets.config.loader import Config
+from traitlets.tests.utils import (
+    check_help_all_output,
+    check_help_output,
+    get_output_error_code,
+)
+
+try:
+    from unittest import mock
+except ImportError:
+    import mock
+
+pjoin = os.path.join
+
+
+class Foo(Configurable):
+
+    i = Integer(0, help="""
+    The integer i.
+
+    Details about i.
+    """).tag(config=True)
+    j = Integer(1, help="The integer j.").tag(config=True)
+    name = Unicode('Brian', help="First name.").tag(config=True)
+    la = List([]).tag(config=True)
+    li = List(Integer()).tag(config=True)
+    fdict = Dict().tag(config=True, multiplicity='+')
+
+
+class Bar(Configurable):
+
+    b = Integer(0, help="The integer b.").tag(config=True)
+    enabled = Bool(True, help="Enable bar.").tag(config=True)
+    tb = Tuple(()).tag(config=True, multiplicity='*')
+    aset = Set().tag(config=True, multiplicity='+')
+    bdict = Dict().tag(config=True)
+    idict = Dict(value_trait=Integer()).tag(config=True)
+    key_dict = Dict(per_key_traits={'i': Integer(), 'b': Bytes()}).tag(config=True)
+
+
+class MyApp(Application):
+
+    name = Unicode('myapp')
+    running = Bool(False, help="Is the app running?").tag(config=True)
+    classes = List([Bar, Foo])
+    config_file = Unicode('', help="Load this config file").tag(config=True)
+
+    warn_tpyo = Unicode("yes the name is wrong on purpose", config=True,
+            help="Should print a warning if `MyApp.warn-typo=...` command is passed")
+
+    aliases = {}
+    aliases.update(Application.aliases)
+    aliases.update({
+                    ('fooi', 'i') : 'Foo.i',
+                    ('j', 'fooj') : ('Foo.j', "`j` terse help msg"),
+                    'name' : 'Foo.name',
+                    'la': 'Foo.la',
+                    'li': 'Foo.li',
+                    'tb': 'Bar.tb',
+                    'D': 'Bar.bdict',
+                    'enabled' : 'Bar.enabled',
+                    'enable' : 'Bar.enabled',
+                    'log-level' : 'Application.log_level',
+                })
+
+    flags = {}
+    flags.update(Application.flags)
+    flags.update({('enable', 'e'):
+                        ({'Bar': {'enabled' : True}},
+                         "Set Bar.enabled to True"),
+                  ('d', 'disable'):
+                        ({'Bar': {'enabled' : False}},
+                         "Set Bar.enabled to False"),
+                  'crit':
+                        ({'Application' : {'log_level' : logging.CRITICAL}},
+                        "set level=CRITICAL"),
+            })
+
+    def init_foo(self):
+        self.foo = Foo(parent=self)
+
+    def init_bar(self):
+        self.bar = Bar(parent=self)
+
+
+def class_to_names(classes):
+    return [klass.__name__ for klass in classes]
+
+
+class TestApplication(TestCase):
+    def test_log(self):
+        stream = StringIO()
+        app = MyApp(log_level=logging.INFO)
+        handler = logging.StreamHandler(stream)
+        # trigger reconstruction of the log formatter
+        app.log.handlers = [handler]
+        app.log_format = "%(message)s"
+        app.log_datefmt = "%Y-%m-%d %H:%M"
+        app.log.info("hello")
+        assert "hello" in stream.getvalue()
+
+    def test_no_eval_cli_text(self):
+        app = MyApp()
+        app.initialize(['--Foo.name=1'])
+        app.init_foo()
+        assert app.foo.name == '1'
+
+    def test_basic(self):
+        app = MyApp()
+        self.assertEqual(app.name, 'myapp')
+        self.assertEqual(app.running, False)
+        self.assertEqual(app.classes, [MyApp, Bar, Foo])
+        self.assertEqual(app.config_file, '')
+
+    def test_mro_discovery(self):
+        app = MyApp()
+
+        self.assertSequenceEqual(class_to_names(app._classes_with_config_traits()),
+                                 ['Application', 'MyApp', 'Bar', 'Foo'])
+        self.assertSequenceEqual(class_to_names(app._classes_inc_parents()),
+                                 ['Configurable', 'LoggingConfigurable', 'SingletonConfigurable',
+                                  'Application', 'MyApp', 'Bar', 'Foo'])
+
+        self.assertSequenceEqual(class_to_names(app._classes_with_config_traits([Application])),
+                                 ['Application'])
+        self.assertSequenceEqual(class_to_names(app._classes_inc_parents([Application])),
+                                 ['Configurable', 'LoggingConfigurable', 'SingletonConfigurable',
+                                  'Application'])
+
+        self.assertSequenceEqual(class_to_names(app._classes_with_config_traits([Foo])),
+                                 ['Foo'])
+        self.assertSequenceEqual(class_to_names(app._classes_inc_parents([Bar])),
+                                 ['Configurable', 'Bar'])
+
+        class MyApp2(Application):  # no defined `classes` attr
+            pass
+
+        self.assertSequenceEqual(class_to_names(app._classes_with_config_traits([Foo])),
+                                 ['Foo'])
+        self.assertSequenceEqual(class_to_names(app._classes_inc_parents([Bar])),
+                                 ['Configurable', 'Bar'])
+
+
+    def test_config(self):
+        app = MyApp()
+        app.parse_command_line([
+            "--i=10",
+            "--Foo.j=10",
+            "--enable=False",
+            "--log-level=50",
+        ])
+        config = app.config
+        print(config)
+        self.assertEqual(config.Foo.i, 10)
+        self.assertEqual(config.Foo.j, 10)
+        self.assertEqual(config.Bar.enabled, False)
+        self.assertEqual(config.MyApp.log_level, 50)
+
+    def test_config_seq_args(self):
+        app = MyApp()
+        app.parse_command_line("--li 1 --li 3 --la 1 --tb AB 2 --Foo.la=ab --Bar.aset S1 --Bar.aset S2 --Bar.aset S1".split())
+        assert app.extra_args == ["2"]
+        config = app.config
+        assert config.Foo.li == [1, 3]
+        assert config.Foo.la == ["1", "ab"]
+        assert config.Bar.tb == ("AB",)
+        self.assertEqual(config.Bar.aset, {"S1", "S2"})
+        app.init_foo()
+        assert app.foo.li == [1, 3]
+        assert app.foo.la == ['1', 'ab']
+        app.init_bar()
+        self.assertEqual(app.bar.aset, {'S1', 'S2'})
+        assert app.bar.tb == ('AB',)
+
+    def test_config_dict_args(self):
+        app = MyApp()
+        app.parse_command_line(
+            "--Foo.fdict a=1 --Foo.fdict b=b --Foo.fdict c=3 "
+            "--Bar.bdict k=1 -D=a=b -D 22=33 "
+            "--Bar.idict k=1 --Bar.idict b=2 --Bar.idict c=3 "
+            .split())
+        fdict = {'a': '1', 'b': 'b', 'c': '3'}
+        bdict = {'k': '1', 'a': 'b', '22': '33'}
+        idict = {'k': 1, 'b': 2, 'c': 3}
+        config = app.config
+        assert config.Bar.idict == idict
+        self.assertDictEqual(config.Foo.fdict, fdict)
+        self.assertDictEqual(config.Bar.bdict, bdict)
+        app.init_foo()
+        self.assertEqual(app.foo.fdict, fdict)
+        app.init_bar()
+        assert app.bar.idict == idict
+        self.assertEqual(app.bar.bdict, bdict)
+
+    def test_config_propagation(self):
+        app = MyApp()
+        app.parse_command_line(["--i=10","--Foo.j=10","--enable=False","--log-level=50"])
+        app.init_foo()
+        app.init_bar()
+        self.assertEqual(app.foo.i, 10)
+        self.assertEqual(app.foo.j, 10)
+        self.assertEqual(app.bar.enabled, False)
+
+    def test_cli_priority(self):
+        """Test that loading config files does not override CLI options"""
+        name = 'config.py'
+        class TestApp(Application):
+            value = Unicode().tag(config=True)
+            config_file_loaded = Bool().tag(config=True)
+            aliases = {'v': 'TestApp.value'}
+        app = TestApp()
+        with TemporaryDirectory() as td:
+            config_file = pjoin(td, name)
+            with open(config_file, 'w') as f:
+                f.writelines([
+                    "c.TestApp.value = 'config file'\n",
+                    "c.TestApp.config_file_loaded = True\n"
+                ])
+
+            app.parse_command_line(['--v=cli'])
+            assert 'value' in app.config.TestApp
+            assert app.config.TestApp.value == 'cli'
+            assert app.value == 'cli'
+
+            app.load_config_file(name, path=[td])
+            assert app.config_file_loaded
+            assert app.config.TestApp.value == 'cli'
+            assert app.value == 'cli'
+
+    def test_ipython_cli_priority(self):
+        # this test is almost entirely redundant with above,
+        # but we can keep it around in case of subtle issues creeping into
+        # the exact sequence IPython follows.
+        name = 'config.py'
+        class TestApp(Application):
+            value = Unicode().tag(config=True)
+            config_file_loaded = Bool().tag(config=True)
+            aliases = {'v': ('TestApp.value', 'some help')}
+        app = TestApp()
+        with TemporaryDirectory() as td:
+            config_file = pjoin(td, name)
+            with open(config_file, 'w') as f:
+                f.writelines([
+                    "c.TestApp.value = 'config file'\n",
+                    "c.TestApp.config_file_loaded = True\n"
+                ])
+            # follow IPython's config-loading sequence to ensure CLI priority is preserved
+            app.parse_command_line(['--v=cli'])
+            # this is where IPython makes a mistake:
+            # it assumes app.config will not be modified,
+            # and storing a reference is storing a copy
+            cli_config = app.config
+            assert 'value' in app.config.TestApp
+            assert app.config.TestApp.value == 'cli'
+            assert app.value == 'cli'
+            app.load_config_file(name, path=[td])
+            assert app.config_file_loaded
+            # enforce cl-opts override config file opts:
+            # this is where IPython makes a mistake: it assumes
+            # that cl_config is a different object, but it isn't.
+            app.update_config(cli_config)
+            assert app.config.TestApp.value == 'cli'
+            assert app.value == 'cli'
+
+    def test_cli_allow_none(self):
+        class App(Application):
+            aliases = {"opt": "App.opt"}
+            opt = Unicode(allow_none=True, config=True)
+
+        app = App()
+        app.parse_command_line(["--opt=None"])
+        assert app.opt is None
+
+    def test_flags(self):
+        app = MyApp()
+        app.parse_command_line(["--disable"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, False)
+
+        app = MyApp()
+        app.parse_command_line(["-d"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, False)
+
+        app = MyApp()
+        app.parse_command_line(["--enable"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, True)
+
+        app = MyApp()
+        app.parse_command_line(["-e"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, True)
+
+    def test_flags_help_msg(self):
+        app = MyApp()
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            app.print_flag_help()
+        hmsg = stdout.getvalue()
+        self.assertRegex(hmsg, "(?<!-)-e, --enable\\b")
+        self.assertRegex(hmsg, "(?<!-)-d, --disable\\b")
+        self.assertIn("Equivalent to: [--Bar.enabled=True]", hmsg)
+        self.assertIn("Equivalent to: [--Bar.enabled=False]", hmsg)
+
+    def test_aliases(self):
+        app = MyApp()
+        app.parse_command_line(["--i=5", "--j=10"])
+        app.init_foo()
+        self.assertEqual(app.foo.i, 5)
+        app.init_foo()
+        self.assertEqual(app.foo.j, 10)
+
+        app = MyApp()
+        app.parse_command_line(["-i=5", "-j=10"])
+        app.init_foo()
+        self.assertEqual(app.foo.i, 5)
+        app.init_foo()
+        self.assertEqual(app.foo.j, 10)
+
+        app = MyApp()
+        app.parse_command_line(["--fooi=5", "--fooj=10"])
+        app.init_foo()
+        self.assertEqual(app.foo.i, 5)
+        app.init_foo()
+        self.assertEqual(app.foo.j, 10)
+
+    def test_aliases_help_msg(self):
+        app = MyApp()
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            app.print_alias_help()
+        hmsg = stdout.getvalue()
+        self.assertRegex(hmsg, "(?<!-)-i, --fooi\\b")
+        self.assertRegex(hmsg, "(?<!-)-j, --fooj\\b")
+        self.assertIn("Equivalent to: [--Foo.i]", hmsg)
+        self.assertIn("Equivalent to: [--Foo.j]", hmsg)
+        self.assertIn("Equivalent to: [--Foo.name]", hmsg)
+
+    def test_flag_clobber(self):
+        """test that setting flags doesn't clobber existing settings"""
+        app = MyApp()
+        app.parse_command_line(["--Bar.b=5", "--disable"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, False)
+        self.assertEqual(app.bar.b, 5)
+        app.parse_command_line(["--enable", "--Bar.b=10"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, True)
+        self.assertEqual(app.bar.b, 10)
+
+    def test_warn_autocorrect(self):
+        stream = StringIO()
+        app = MyApp(log_level=logging.INFO)
+        app.log.handlers = [logging.StreamHandler(stream)]
+
+        cfg = Config()
+        cfg.MyApp.warn_typo = "WOOOO"
+        app.config = cfg
+
+        self.assertIn("warn_typo", stream.getvalue())
+        self.assertIn("warn_tpyo", stream.getvalue())
+
+
+    def test_flatten_flags(self):
+        cfg = Config()
+        cfg.MyApp.log_level = logging.WARN
+        app = MyApp()
+        app.update_config(cfg)
+        self.assertEqual(app.log_level, logging.WARN)
+        self.assertEqual(app.config.MyApp.log_level, logging.WARN)
+        app.initialize(["--crit"])
+        self.assertEqual(app.log_level, logging.CRITICAL)
+        # this would be app.config.Application.log_level if it failed:
+        self.assertEqual(app.config.MyApp.log_level, logging.CRITICAL)
+
+    def test_flatten_aliases(self):
+        cfg = Config()
+        cfg.MyApp.log_level = logging.WARN
+        app = MyApp()
+        app.update_config(cfg)
+        self.assertEqual(app.log_level, logging.WARN)
+        self.assertEqual(app.config.MyApp.log_level, logging.WARN)
+        app.initialize(["--log-level", "CRITICAL"])
+        self.assertEqual(app.log_level, logging.CRITICAL)
+        # this would be app.config.Application.log_level if it failed:
+        self.assertEqual(app.config.MyApp.log_level, "CRITICAL")
+
+    def test_extra_args(self):
+
+        app = MyApp()
+        app.parse_command_line(["--Bar.b=5", 'extra', 'args', "--disable"])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, False)
+        self.assertEqual(app.bar.b, 5)
+        self.assertEqual(app.extra_args, ['extra', 'args'])
+
+        app = MyApp()
+        app.parse_command_line(["--Bar.b=5", '--', 'extra', "--disable", 'args'])
+        app.init_bar()
+        self.assertEqual(app.bar.enabled, True)
+        self.assertEqual(app.bar.b, 5)
+        self.assertEqual(app.extra_args, ['extra', '--disable', 'args'])
+
+        app = MyApp()
+        app.parse_command_line(
+            ["--disable", "--la", "-", "-", "--Bar.b=1", "--", "-", "extra"]
+        )
+        self.assertEqual(app.extra_args, ["-", "-", "extra"])
+
+    def test_unicode_argv(self):
+        app = MyApp()
+        app.parse_command_line(['ünîcødé'])
+
+    def test_document_config_option(self):
+        app = MyApp()
+        app.document_config_options()
+
+    def test_generate_config_file(self):
+        app = MyApp()
+        assert 'The integer b.' in app.generate_config_file()
+
+    def test_generate_config_file_classes_to_include(self):
+        class NotInConfig(HasTraits):
+            from_hidden = Unicode('x', help="""From hidden class
+            
+            Details about from_hidden.
+            """).tag(config=True)
+
+        class NoTraits(Foo, Bar, NotInConfig):
+            pass
+
+        app = MyApp()
+        app.classes.append(NoTraits)
+
+        conf_txt = app.generate_config_file()
+        print(conf_txt)
+        self.assertIn('The integer b.', conf_txt)
+        self.assertIn('# Foo(Configurable)', conf_txt)
+        self.assertNotIn('# Configurable', conf_txt)
+        self.assertIn('# NoTraits(Foo, Bar)', conf_txt)
+
+        # inherited traits, parent in class list:
+        self.assertIn('# c.NoTraits.i', conf_txt)
+        self.assertIn('# c.NoTraits.j', conf_txt)
+        self.assertIn('# c.NoTraits.n', conf_txt)
+        self.assertIn('#  See also: Foo.j', conf_txt)
+        self.assertIn('#  See also: Bar.b', conf_txt)
+        self.assertEqual(conf_txt.count('Details about i.'), 1)
+
+        # inherited traits, parent not in class list:
+        self.assertIn("# c.NoTraits.from_hidden", conf_txt)
+        self.assertNotIn('#  See also: NotInConfig.', conf_txt)
+        self.assertEqual(conf_txt.count('Details about from_hidden.'), 1)
+        self.assertNotIn("NotInConfig", conf_txt)
+
+    def test_multi_file(self):
+        app = MyApp()
+        app.log = logging.getLogger()
+        name = 'config.py'
+        with TemporaryDirectory('_1') as td1:
+            with open(pjoin(td1, name), 'w') as f1:
+                f1.write("get_config().MyApp.Bar.b = 1")
+            with TemporaryDirectory('_2') as td2:
+                with open(pjoin(td2, name), 'w') as f2:
+                    f2.write("get_config().MyApp.Bar.b = 2")
+                app.load_config_file(name, path=[td2, td1])
+                app.init_bar()
+                self.assertEqual(app.bar.b, 2)
+                app.load_config_file(name, path=[td1, td2])
+                app.init_bar()
+                self.assertEqual(app.bar.b, 1)
+
+    @mark.skipif(not hasattr(TestCase, 'assertLogs'), reason='requires TestCase.assertLogs')
+    def test_log_collisions(self):
+        app = MyApp()
+        app.log = logging.getLogger()
+        app.log.setLevel(logging.INFO)
+        name = 'config'
+        with TemporaryDirectory('_1') as td:
+            with open(pjoin(td, name + '.py'), 'w') as f:
+                f.write("get_config().Bar.b = 1")
+            with open(pjoin(td, name + '.json'), 'w') as f:
+                json.dump({
+                    'Bar': {
+                        'b': 2
+                    }
+                }, f)
+            with self.assertLogs(app.log, logging.WARNING) as captured:
+                app.load_config_file(name, path=[td])
+                app.init_bar()
+        assert app.bar.b == 2
+        output = '\n'.join(captured.output)
+        assert 'Collision' in output
+        assert '1 ignored, using 2' in output
+        assert pjoin(td, name + '.py') in output
+        assert pjoin(td, name + '.json') in output
+
+    @mark.skipif(not hasattr(TestCase, 'assertLogs'), reason='requires TestCase.assertLogs')
+    def test_log_bad_config(self):
+        app = MyApp()
+        app.log = logging.getLogger()
+        name = 'config.py'
+        with TemporaryDirectory() as td:
+            with open(pjoin(td, name), 'w') as f:
+                f.write("syntax error()")
+            with self.assertLogs(app.log, logging.ERROR) as captured:
+                app.load_config_file(name, path=[td])
+        output = '\n'.join(captured.output)
+        self.assertIn('SyntaxError', output)
+
+    def test_raise_on_bad_config(self):
+        app = MyApp()
+        app.raise_config_file_errors = True
+        app.log = logging.getLogger()
+        name = 'config.py'
+        with TemporaryDirectory() as td:
+            with open(pjoin(td, name), 'w') as f:
+                f.write("syntax error()")
+            with self.assertRaises(SyntaxError):
+                app.load_config_file(name, path=[td])
+
+    def test_subcommands_instanciation(self):
+        """Try all ways to specify how to create sub-apps."""
+        app = Root.instance()
+        app.parse_command_line(['sub1'])
+
+        self.assertIsInstance(app.subapp, Sub1)
+        ## Check parent hierarchy.
+        self.assertIs(app.subapp.parent, app)
+
+        Root.clear_instance()
+        Sub1.clear_instance()  # Otherwise, replaced spuriously and hierarchy check fails.
+        app = Root.instance()
+
+        app.parse_command_line(['sub1', 'sub2'])
+        self.assertIsInstance(app.subapp, Sub1)
+        self.assertIsInstance(app.subapp.subapp, Sub2)
+        ## Check parent hierarchy.
+        self.assertIs(app.subapp.parent, app)
+        self.assertIs(app.subapp.subapp.parent, app.subapp)
+
+        Root.clear_instance()
+        Sub1.clear_instance()  # Otherwise, replaced spuriously and hierarchy check fails.
+        app = Root.instance()
+
+        app.parse_command_line(['sub1', 'sub3'])
+        self.assertIsInstance(app.subapp, Sub1)
+        self.assertIsInstance(app.subapp.subapp, Sub3)
+        self.assertTrue(app.subapp.subapp.flag)               # Set by factory.
+        ## Check parent hierarchy.
+        self.assertIs(app.subapp.parent, app)
+        self.assertIs(app.subapp.subapp.parent, app.subapp)     # Set by factory.
+
+    def test_loaded_config_files(self):
+        app = MyApp()
+        app.log = logging.getLogger()
+        name = 'config.py'
+        with TemporaryDirectory('_1') as td1:
+            config_file = pjoin(td1, name)
+            with open(config_file, 'w') as f:
+                f.writelines([
+                    "c.MyApp.running = True\n"
+                ])
+
+            app.load_config_file(name, path=[td1])
+            self.assertEqual(len(app.loaded_config_files), 1)
+            self.assertEqual(app.loaded_config_files[0], config_file)
+
+            app.start()
+            self.assertEqual(app.running, True)
+
+            # emulate an app that allows dynamic updates and update config file
+            with open(config_file, 'w') as f:
+                f.writelines([
+                    "c.MyApp.running = False\n"
+                ])
+
+            # reload and verify update, and that loaded_configs was not increased
+            app.load_config_file(name, path=[td1])
+            self.assertEqual(len(app.loaded_config_files), 1)
+            self.assertEqual(app.running, False)
+
+            # Attempt to update, ensure error...
+            with self.assertRaises(AttributeError):
+                app.loaded_config_files = "/foo"
+
+            # ensure it can't be udpated via append
+            app.loaded_config_files.append("/bar")
+            self.assertEqual(len(app.loaded_config_files), 1)
+
+            # repeat to ensure no unexpected changes occurred
+            app.load_config_file(name, path=[td1])
+            self.assertEqual(len(app.loaded_config_files), 1)
+            self.assertEqual(app.running, False)
+
+
+def test_cli_multi_scalar(caplog):
+    class App(Application):
+        aliases = {"opt": "App.opt"}
+        opt = Unicode(config=True)
+
+    app = App(log=logging.getLogger())
+    with pytest.raises(SystemExit):
+        app.parse_command_line(["--opt", "1", "--opt", "2"])
+    record = caplog.get_records("call")[-1]
+    message = record.message
+
+    assert "Error loading argument" in message
+    assert "App.opt=['1', '2']" in message
+    assert "opt only accepts one value" in message
+    assert record.levelno == logging.CRITICAL
+
+
+class Root(Application):
+    subcommands = {
+        'sub1': ('traitlets.config.tests.test_application.Sub1', 'import string'),
+    }
+
+
+class Sub3(Application):
+    flag = Bool(False)
+
+
+class Sub2(Application):
+    pass
+
+
+class Sub1(Application):
+    subcommands = {
+        'sub2': (Sub2, 'Application class'),
+        'sub3': (lambda root: Sub3(parent=root, flag=True), 'factory'),
+    }
+
+
+class DeprecatedApp(Application):
+    override_called = False
+    parent_called = False
+    def _config_changed(self, name, old, new):
+        self.override_called = True
+        def _capture(*args):
+            self.parent_called = True
+        with mock.patch.object(self.log, 'debug', _capture):
+            super(DeprecatedApp, self)._config_changed(name, old, new)
+
+
+def test_deprecated_notifier():
+    app = DeprecatedApp()
+    assert not app.override_called
+    assert not app.parent_called
+    app.config = Config({'A': {'b': 'c'}})
+    assert app.override_called
+    assert app.parent_called
+
+
+def test_help_output():
+    check_help_output(__name__)
+
+
+def test_help_all_output():
+    check_help_all_output(__name__)
+
+
+def test_show_config_cli():
+    out, err, ec = get_output_error_code([sys.executable, '-m', __name__, '--show-config'])
+    assert ec == 0
+    assert 'show_config' not in out
+
+
+def test_show_config_json_cli():
+    out, err, ec = get_output_error_code([sys.executable, '-m', __name__, '--show-config-json'])
+    assert ec == 0
+    assert 'show_config' not in out
+
+
+def test_show_config(capsys):
+    cfg = Config()
+    cfg.MyApp.i = 5
+    # don't show empty
+    cfg.OtherApp
+
+    app = MyApp(config=cfg, show_config=True)
+    app.start()
+    out, err = capsys.readouterr()
+    assert 'MyApp' in out
+    assert 'i = 5' in out
+    assert 'OtherApp' not in out
+
+
+def test_show_config_json(capsys):
+    cfg = Config()
+    cfg.MyApp.i = 5
+    cfg.OtherApp
+
+    app = MyApp(config=cfg, show_config_json=True)
+    app.start()
+    out, err = capsys.readouterr()
+    displayed = json.loads(out)
+    assert Config(displayed) == cfg
+
+
+def test_deep_alias():
+    from traitlets.config import Application, Configurable
+    from traitlets import Int
+
+    class Foo(Configurable):
+        val = Int(default_value=5).tag(config=True)
+
+    class Bar(Configurable):
+
+        def __init__(self, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            self.foo = Foo(parent=self)
+
+    class TestApp(Application):
+        name = 'test'
+
+        aliases = {'val': 'Bar.Foo.val'}
+        classes = [Foo, Bar]
+
+        def initialize(self, *args, **kwargs):
+            super().initialize(*args, **kwargs)
+            self.bar = Bar(parent=self)
+
+    app = TestApp()
+    app.initialize(['--val=10'])
+    assert app.bar.foo.val == 10
+    assert len(list(app.emit_alias_help())) > 0
+
+
+if __name__ == '__main__':
+    # for test_help_output:
+    MyApp.launch_instance()

.venv/lib/python3.8/site-packages/traitlets/config/tests/test_configurable.py

@@ -0,0 +1,680 @@
+"""Tests for traitlets.config.configurable"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import logging
+from unittest import TestCase
+
+from pytest import mark
+
+from traitlets.config.application import Application
+from traitlets.config.configurable import (
+    Configurable,
+    LoggingConfigurable,
+    SingletonConfigurable,
+)
+from traitlets.log import get_logger
+from traitlets.traitlets import (
+    Integer, Float, Unicode, List, Dict, Set, Enum, FuzzyEnum,
+    CaselessStrEnum, _deprecations_shown, validate,
+)
+
+from traitlets.config.loader import Config
+
+from ...tests._warnings import expected_warnings
+
+class MyConfigurable(Configurable):
+    a = Integer(1, help="The integer a.").tag(config=True)
+    b = Float(1.0, help="The integer b.").tag(config=True)
+    c = Unicode('no config')
+
+
+mc_help = """MyConfigurable(Configurable) options
+------------------------------------
+--MyConfigurable.a=<Integer>
+    The integer a.
+    Default: 1
+--MyConfigurable.b=<Float>
+    The integer b.
+    Default: 1.0"""
+
+mc_help_inst="""MyConfigurable(Configurable) options
+------------------------------------
+--MyConfigurable.a=<Integer>
+    The integer a.
+    Current: 5
+--MyConfigurable.b=<Float>
+    The integer b.
+    Current: 4.0"""
+
+# On Python 3, the Integer trait is a synonym for Int
+mc_help = mc_help.replace("<Integer>", "<Int>")
+mc_help_inst = mc_help_inst.replace("<Integer>", "<Int>")
+
+class Foo(Configurable):
+    a = Integer(0, help="The integer a.").tag(config=True)
+    b = Unicode('nope').tag(config=True)
+    flist = List([]).tag(config=True)
+    fdict = Dict().tag(config=True)
+
+
+class Bar(Foo):
+    b = Unicode('gotit', help="The string b.").tag(config=False)
+    c = Float(help="The string c.").tag(config=True)
+    bset = Set([]).tag(config=True, multiplicity='+')
+    bset_values = Set([2,1,5]).tag(config=True, multiplicity='+')
+    bdict = Dict().tag(config=True, multiplicity='+')
+    bdict_values = Dict({1:'a','0':'b',5:'c'}).tag(config=True, multiplicity='+')
+
+foo_help="""Foo(Configurable) options
+-------------------------
+--Foo.a=<Int>
+    The integer a.
+    Default: 0
+--Foo.b=<Unicode>
+    Default: 'nope'
+--Foo.fdict=<key-1>=<value-1>...
+    Default: {}
+--Foo.flist=<list-item-1>...
+    Default: []"""
+
+bar_help="""Bar(Foo) options
+----------------
+--Bar.a=<Int>
+    The integer a.
+    Default: 0
+--Bar.bdict <key-1>=<value-1>...
+    Default: {}
+--Bar.bdict_values <key-1>=<value-1>...
+    Default: {1: 'a', '0': 'b', 5: 'c'}
+--Bar.bset <set-item-1>...
+    Default: set()
+--Bar.bset_values <set-item-1>...
+    Default: {1, 2, 5}
+--Bar.c=<Float>
+    The string c.
+    Default: 0.0
+--Bar.fdict=<key-1>=<value-1>...
+    Default: {}
+--Bar.flist=<list-item-1>...
+    Default: []"""
+
+
+class TestConfigurable(TestCase):
+
+    def test_default(self):
+        c1 = Configurable()
+        c2 = Configurable(config=c1.config)
+        c3 = Configurable(config=c2.config)
+        self.assertEqual(c1.config, c2.config)
+        self.assertEqual(c2.config, c3.config)
+
+    def test_custom(self):
+        config = Config()
+        config.foo = 'foo'
+        config.bar = 'bar'
+        c1 = Configurable(config=config)
+        c2 = Configurable(config=c1.config)
+        c3 = Configurable(config=c2.config)
+        self.assertEqual(c1.config, config)
+        self.assertEqual(c2.config, config)
+        self.assertEqual(c3.config, config)
+        # Test that copies are not made
+        self.assertTrue(c1.config is config)
+        self.assertTrue(c2.config is config)
+        self.assertTrue(c3.config is config)
+        self.assertTrue(c1.config is c2.config)
+        self.assertTrue(c2.config is c3.config)
+
+    def test_inheritance(self):
+        config = Config()
+        config.MyConfigurable.a = 2
+        config.MyConfigurable.b = 2.0
+        c1 = MyConfigurable(config=config)
+        c2 = MyConfigurable(config=c1.config)
+        self.assertEqual(c1.a, config.MyConfigurable.a)
+        self.assertEqual(c1.b, config.MyConfigurable.b)
+        self.assertEqual(c2.a, config.MyConfigurable.a)
+        self.assertEqual(c2.b, config.MyConfigurable.b)
+
+    def test_parent(self):
+        config = Config()
+        config.Foo.a = 10
+        config.Foo.b = "wow"
+        config.Bar.b = 'later'
+        config.Bar.c = 100.0
+        f = Foo(config=config)
+        with expected_warnings(['`b` not recognized']):
+            b = Bar(config=f.config)
+        self.assertEqual(f.a, 10)
+        self.assertEqual(f.b, 'wow')
+        self.assertEqual(b.b, 'gotit')
+        self.assertEqual(b.c, 100.0)
+
+    def test_override1(self):
+        config = Config()
+        config.MyConfigurable.a = 2
+        config.MyConfigurable.b = 2.0
+        c = MyConfigurable(a=3, config=config)
+        self.assertEqual(c.a, 3)
+        self.assertEqual(c.b, config.MyConfigurable.b)
+        self.assertEqual(c.c, 'no config')
+
+    def test_override2(self):
+        config = Config()
+        config.Foo.a = 1
+        config.Bar.b = 'or'  # Up above b is config=False, so this won't do it.
+        config.Bar.c = 10.0
+        with expected_warnings(['`b` not recognized']):
+            c = Bar(config=config)
+        self.assertEqual(c.a, config.Foo.a)
+        self.assertEqual(c.b, 'gotit')
+        self.assertEqual(c.c, config.Bar.c)
+        with expected_warnings(['`b` not recognized']):
+            c = Bar(a=2, b='and', c=20.0, config=config)
+        self.assertEqual(c.a, 2)
+        self.assertEqual(c.b, 'and')
+        self.assertEqual(c.c, 20.0)
+
+    def test_help(self):
+        self.assertEqual(MyConfigurable.class_get_help(), mc_help)
+        self.assertEqual(Foo.class_get_help(), foo_help)
+        self.assertEqual(Bar.class_get_help(), bar_help)
+
+    def test_help_inst(self):
+        inst = MyConfigurable(a=5, b=4)
+        self.assertEqual(MyConfigurable.class_get_help(inst), mc_help_inst)
+
+    def test_generated_config_enum_comments(self):
+        class MyConf(Configurable):
+            an_enum = Enum('Choice1 choice2'.split(),
+                           help="Many choices.").tag(config=True)
+
+        help_str = "Many choices."
+        enum_choices_str = "Choices: any of ['Choice1', 'choice2']"
+        rst_choices_str = "MyConf.an_enum : any of ``'Choice1'``|``'choice2'``"
+        or_none_str = "or None"
+
+        cls_help = MyConf.class_get_help()
+
+        self.assertIn(help_str, cls_help)
+        self.assertIn(enum_choices_str, cls_help)
+        self.assertNotIn(or_none_str, cls_help)
+
+        cls_cfg = MyConf.class_config_section()
+
+        self.assertIn(help_str, cls_cfg)
+        self.assertIn(enum_choices_str, cls_cfg)
+        self.assertNotIn(or_none_str, cls_help)
+        ## Check order of Help-msg <--> Choices sections
+        self.assertGreater(cls_cfg.index(enum_choices_str),
+                           cls_cfg.index(help_str))
+
+        rst_help = MyConf.class_config_rst_doc()
+
+        self.assertIn(help_str, rst_help)
+        self.assertIn(rst_choices_str, rst_help)
+        self.assertNotIn(or_none_str, rst_help)
+
+        class MyConf2(Configurable):
+            an_enum = Enum('Choice1 choice2'.split(),
+                           allow_none=True,
+                           default_value='choice2',
+                           help="Many choices.").tag(config=True)
+
+        defaults_str = "Default: 'choice2'"
+
+        cls2_msg = MyConf2.class_get_help()
+
+        self.assertIn(help_str, cls2_msg)
+        self.assertIn(enum_choices_str, cls2_msg)
+        self.assertIn(or_none_str, cls2_msg)
+        self.assertIn(defaults_str, cls2_msg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls2_msg.index(defaults_str),
+                           cls2_msg.index(enum_choices_str))
+
+        cls2_cfg = MyConf2.class_config_section()
+
+        self.assertIn(help_str, cls2_cfg)
+        self.assertIn(enum_choices_str, cls2_cfg)
+        self.assertIn(or_none_str, cls2_cfg)
+        self.assertIn(defaults_str, cls2_cfg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls2_cfg.index(defaults_str),
+                           cls2_cfg.index(enum_choices_str))
+
+    def test_generated_config_strenum_comments(self):
+        help_str = "Many choices."
+        defaults_str = "Default: 'choice2'"
+        or_none_str = "or None"
+
+        class MyConf3(Configurable):
+            an_enum = CaselessStrEnum('Choice1 choice2'.split(),
+                                      allow_none=True,
+                                      default_value='choice2',
+                                      help="Many choices.").tag(config=True)
+
+        enum_choices_str = ("Choices: any of ['Choice1', 'choice2'] "
+                            "(case-insensitive)")
+
+        cls3_msg = MyConf3.class_get_help()
+
+        self.assertIn(help_str, cls3_msg)
+        self.assertIn(enum_choices_str, cls3_msg)
+        self.assertIn(or_none_str, cls3_msg)
+        self.assertIn(defaults_str, cls3_msg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls3_msg.index(defaults_str),
+                           cls3_msg.index(enum_choices_str))
+
+        cls3_cfg = MyConf3.class_config_section()
+
+        self.assertIn(help_str, cls3_cfg)
+        self.assertIn(enum_choices_str, cls3_cfg)
+        self.assertIn(or_none_str, cls3_cfg)
+        self.assertIn(defaults_str, cls3_cfg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls3_cfg.index(defaults_str),
+                           cls3_cfg.index(enum_choices_str))
+
+        class MyConf4(Configurable):
+            an_enum = FuzzyEnum('Choice1 choice2'.split(),
+                                allow_none=True,
+                                default_value='choice2',
+                                help="Many choices.").tag(config=True)
+
+        enum_choices_str = ("Choices: any case-insensitive prefix "
+                            "of ['Choice1', 'choice2']")
+
+        cls4_msg = MyConf4.class_get_help()
+
+        self.assertIn(help_str, cls4_msg)
+        self.assertIn(enum_choices_str, cls4_msg)
+        self.assertIn(or_none_str, cls4_msg)
+        self.assertIn(defaults_str, cls4_msg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls4_msg.index(defaults_str),
+                           cls4_msg.index(enum_choices_str))
+
+        cls4_cfg = MyConf4.class_config_section()
+
+        self.assertIn(help_str, cls4_cfg)
+        self.assertIn(enum_choices_str, cls4_cfg)
+        self.assertIn(or_none_str, cls4_cfg)
+        self.assertIn(defaults_str, cls4_cfg)
+        ## Check order of Default <--> Choices sections
+        self.assertGreater(cls4_cfg.index(defaults_str),
+                           cls4_cfg.index(enum_choices_str))
+
+
+
+class TestSingletonConfigurable(TestCase):
+
+    def test_instance(self):
+        class Foo(SingletonConfigurable): pass
+        self.assertEqual(Foo.initialized(), False)
+        foo = Foo.instance()
+        self.assertEqual(Foo.initialized(), True)
+        self.assertEqual(foo, Foo.instance())
+        self.assertEqual(SingletonConfigurable._instance, None)
+
+    def test_inheritance(self):
+        class Bar(SingletonConfigurable): pass
+        class Bam(Bar): pass
+        self.assertEqual(Bar.initialized(), False)
+        self.assertEqual(Bam.initialized(), False)
+        bam = Bam.instance()
+        self.assertEqual(Bar.initialized(), True)
+        self.assertEqual(Bam.initialized(), True)
+        self.assertEqual(bam, Bam._instance)
+        self.assertEqual(bam, Bar._instance)
+        self.assertEqual(SingletonConfigurable._instance, None)
+
+
+class TestLoggingConfigurable(TestCase):
+
+    def test_parent_logger(self):
+        class Parent(LoggingConfigurable): pass
+        class Child(LoggingConfigurable): pass
+        log = get_logger().getChild("TestLoggingConfigurable")
+
+        parent = Parent(log=log)
+        child = Child(parent=parent)
+        self.assertEqual(parent.log, log)
+        self.assertEqual(child.log, log)
+
+        parent = Parent()
+        child = Child(parent=parent, log=log)
+        self.assertEqual(parent.log, get_logger())
+        self.assertEqual(child.log, log)
+
+    def test_parent_not_logging_configurable(self):
+        class Parent(Configurable): pass
+        class Child(LoggingConfigurable): pass
+        parent = Parent()
+        child = Child(parent=parent)
+        self.assertEqual(child.log, get_logger())
+
+
+class MyParent(Configurable):
+    pass
+
+class MyParent2(MyParent):
+    pass
+
+class TestParentConfigurable(TestCase):
+
+    def test_parent_config(self):
+        cfg = Config({
+            'MyParent' : {
+                'MyConfigurable' : {
+                    'b' : 2.0,
+                }
+            }
+        })
+        parent = MyParent(config=cfg)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent.MyConfigurable.b)
+
+    def test_parent_inheritance(self):
+        cfg = Config({
+            'MyParent' : {
+                'MyConfigurable' : {
+                    'b' : 2.0,
+                }
+            }
+        })
+        parent = MyParent2(config=cfg)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent.MyConfigurable.b)
+
+    def test_multi_parent(self):
+        cfg = Config({
+            'MyParent2' : {
+                'MyParent' : {
+                    'MyConfigurable' : {
+                        'b' : 2.0,
+                    }
+                },
+                # this one shouldn't count
+                'MyConfigurable' : {
+                    'b' : 3.0,
+                },
+            }
+        })
+        parent2 = MyParent2(config=cfg)
+        parent = MyParent(parent=parent2)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent2.MyParent.MyConfigurable.b)
+
+    def test_parent_priority(self):
+        cfg = Config({
+            'MyConfigurable' : {
+                'b' : 2.0,
+            },
+            'MyParent' : {
+                'MyConfigurable' : {
+                    'b' : 3.0,
+                }
+            },
+            'MyParent2' : {
+                'MyConfigurable' : {
+                    'b' : 4.0,
+                }
+            }
+        })
+        parent = MyParent2(config=cfg)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent2.MyConfigurable.b)
+
+    def test_multi_parent_priority(self):
+        cfg = Config({
+            'MyConfigurable': {
+                'b': 2.0,
+            },
+            'MyParent': {
+                'MyConfigurable': {
+                    'b': 3.0,
+                },
+            },
+            'MyParent2': {
+                'MyConfigurable': {
+                    'b': 4.0,
+                },
+                'MyParent': {
+                    'MyConfigurable': {
+                        'b': 5.0,
+                    },
+                },
+            },
+        })
+        parent2 = MyParent2(config=cfg)
+        parent = MyParent2(parent=parent2)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent2.MyParent.MyConfigurable.b)
+
+class Containers(Configurable):
+    lis = List().tag(config=True)
+    def _lis_default(self):
+        return [-1]
+
+    s = Set().tag(config=True)
+    def _s_default(self):
+        return {'a'}
+
+    d = Dict().tag(config=True)
+    def _d_default(self):
+        return {'a' : 'b'}
+
+class TestConfigContainers(TestCase):
+    def test_extend(self):
+        c = Config()
+        c.Containers.lis.extend(list(range(5)))
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, list(range(-1,5)))
+
+    def test_insert(self):
+        c = Config()
+        c.Containers.lis.insert(0, 'a')
+        c.Containers.lis.insert(1, 'b')
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, ['a', 'b', -1])
+
+    def test_prepend(self):
+        c = Config()
+        c.Containers.lis.prepend([1,2])
+        c.Containers.lis.prepend([2,3])
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, [2,3,1,2,-1])
+
+    def test_prepend_extend(self):
+        c = Config()
+        c.Containers.lis.prepend([1,2])
+        c.Containers.lis.extend([2,3])
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, [1,2,-1,2,3])
+
+    def test_append_extend(self):
+        c = Config()
+        c.Containers.lis.append([1,2])
+        c.Containers.lis.extend([2,3])
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, [-1,[1,2],2,3])
+
+    def test_extend_append(self):
+        c = Config()
+        c.Containers.lis.extend([2,3])
+        c.Containers.lis.append([1,2])
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, [-1,2,3,[1,2]])
+
+    def test_insert_extend(self):
+        c = Config()
+        c.Containers.lis.insert(0, 1)
+        c.Containers.lis.extend([2,3])
+        obj = Containers(config=c)
+        self.assertEqual(obj.lis, [1,-1,2,3])
+
+    def test_set_update(self):
+        c = Config()
+        c.Containers.s.update({0,1,2})
+        c.Containers.s.update({3})
+        obj = Containers(config=c)
+        self.assertEqual(obj.s, {'a', 0, 1, 2, 3})
+
+    def test_dict_update(self):
+        c = Config()
+        c.Containers.d.update({'c' : 'd'})
+        c.Containers.d.update({'e' : 'f'})
+        obj = Containers(config=c)
+        self.assertEqual(obj.d, {'a':'b', 'c':'d', 'e':'f'})
+
+    def test_update_twice(self):
+        c = Config()
+        c.MyConfigurable.a = 5
+        m = MyConfigurable(config=c)
+        self.assertEqual(m.a, 5)
+
+        c2 = Config()
+        c2.MyConfigurable.a = 10
+        m.update_config(c2)
+        self.assertEqual(m.a, 10)
+
+        c2.MyConfigurable.a = 15
+        m.update_config(c2)
+        self.assertEqual(m.a, 15)
+
+    def test_update_self(self):
+        """update_config with same config object still triggers config_changed"""
+        c = Config()
+        c.MyConfigurable.a = 5
+        m = MyConfigurable(config=c)
+        self.assertEqual(m.a, 5)
+        c.MyConfigurable.a = 10
+        m.update_config(c)
+        self.assertEqual(m.a, 10)
+
+    def test_config_default(self):
+        class SomeSingleton(SingletonConfigurable):
+            pass
+
+        class DefaultConfigurable(Configurable):
+            a = Integer().tag(config=True)
+            def _config_default(self):
+                if SomeSingleton.initialized():
+                    return SomeSingleton.instance().config
+                return Config()
+
+        c = Config()
+        c.DefaultConfigurable.a = 5
+
+        d1 = DefaultConfigurable()
+        self.assertEqual(d1.a, 0)
+
+        single = SomeSingleton.instance(config=c)
+
+        d2 = DefaultConfigurable()
+        self.assertIs(d2.config, single.config)
+        self.assertEqual(d2.a, 5)
+
+    def test_config_default_deprecated(self):
+        """Make sure configurables work even with the deprecations in traitlets"""
+        class SomeSingleton(SingletonConfigurable):
+            pass
+
+        # reset deprecation limiter
+        _deprecations_shown.clear()
+        with expected_warnings([]):
+            class DefaultConfigurable(Configurable):
+                a = Integer(config=True)
+                def _config_default(self):
+                    if SomeSingleton.initialized():
+                        return SomeSingleton.instance().config
+                    return Config()
+
+        c = Config()
+        c.DefaultConfigurable.a = 5
+
+        d1 = DefaultConfigurable()
+        self.assertEqual(d1.a, 0)
+
+        single = SomeSingleton.instance(config=c)
+
+        d2 = DefaultConfigurable()
+        self.assertIs(d2.config, single.config)
+        self.assertEqual(d2.a, 5)
+
+    def test_kwarg_config_priority(self):
+        # a, c set in kwargs
+        # a, b set in config
+        # verify that:
+        # - kwargs are set before config
+        # - kwargs have priority over config
+        class A(Configurable):
+            a = Unicode('default', config=True)
+            b = Unicode('default', config=True)
+            c = Unicode('default', config=True)
+            c_during_config = Unicode('never')
+            @validate('b')
+            def _record_c(self, proposal):
+                # setting b from config records c's value at the time
+                self.c_during_config = self.c
+                return proposal.value
+
+        cfg = Config()
+        cfg.A.a = 'a-config'
+        cfg.A.b = 'b-config'
+        obj = A(a='a-kwarg', c='c-kwarg', config=cfg)
+        assert obj.a == 'a-kwarg'
+        assert obj.b == 'b-config'
+        assert obj.c == 'c-kwarg'
+        assert obj.c_during_config == 'c-kwarg'
+
+
+class TestLogger(TestCase):
+
+    class A(LoggingConfigurable):
+            foo = Integer(config=True)
+            bar = Integer(config=True)
+            baz = Integer(config=True)
+
+    @mark.skipif(not hasattr(TestCase, 'assertLogs'), reason='requires TestCase.assertLogs')
+    def test_warn_match(self):
+        logger = logging.getLogger('test_warn_match')
+        cfg = Config({'A': {'bat': 5}})
+        with self.assertLogs(logger, logging.WARNING) as captured:
+            TestLogger.A(config=cfg, log=logger)
+
+        output = '\n'.join(captured.output)
+        self.assertIn('Did you mean one of: `bar, baz`?', output)
+        self.assertIn('Config option `bat` not recognized by `A`.', output)
+
+        cfg = Config({'A': {'fool': 5}})
+        with self.assertLogs(logger, logging.WARNING) as captured:
+            TestLogger.A(config=cfg, log=logger)
+
+        output = '\n'.join(captured.output)
+        self.assertIn('Config option `fool` not recognized by `A`.', output)
+        self.assertIn('Did you mean `foo`?', output)
+
+        cfg = Config({'A': {'totally_wrong': 5}})
+        with self.assertLogs(logger, logging.WARNING) as captured:
+            TestLogger.A(config=cfg, log=logger)
+
+        output = '\n'.join(captured.output)
+        self.assertIn('Config option `totally_wrong` not recognized by `A`.', output)
+        self.assertNotIn('Did you mean', output)
+
+    def test_logger_adapter(self):
+        logger = logging.getLogger("test_logger_adapter")
+        adapter = logging.LoggerAdapter(logger, {"key": "adapted"})
+
+        with self.assertLogs(logger, logging.INFO) as captured:
+            app = Application(log=adapter, log_level=logging.INFO)
+            app.log_format = "%(key)s %(message)s"
+            app.log.info("test message")
+
+        output = "\n".join(captured.output)
+        assert "adapted test message" in output

.venv/lib/python3.8/site-packages/traitlets/config/tests/test_loader.py

@@ -0,0 +1,754 @@
+# encoding: utf-8
+"""Tests for traitlets.config.loader"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import copy
+import os
+import pickle
+from itertools import chain
+from tempfile import mkstemp
+from unittest import TestCase
+
+import pytest
+
+from traitlets.config.loader import (
+    Config,
+    LazyConfigValue,
+    PyFileConfigLoader,
+    JSONFileConfigLoader,
+    KeyValueConfigLoader,
+    ArgParseConfigLoader,
+    KVArgParseConfigLoader,
+)
+from traitlets import (
+    List,
+    Tuple,
+    Dict,
+    Unicode,
+    Integer,
+)
+from traitlets.config import Configurable
+
+
+pyfile = """
+c = get_config()
+c.a=10
+c.b=20
+c.Foo.Bar.value=10
+c.Foo.Bam.value=list(range(10))
+c.D.C.value='hi there'
+"""
+
+json1file = """
+{
+  "version": 1,
+  "a": 10,
+  "b": 20,
+  "Foo": {
+    "Bam": {
+      "value": [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
+    },
+    "Bar": {
+      "value": 10
+    }
+  },
+  "D": {
+    "C": {
+      "value": "hi there"
+    }
+  }
+}
+"""
+
+# should not load
+json2file = """
+{
+  "version": 2
+}
+"""
+
+import logging
+log = logging.getLogger('devnull')
+log.setLevel(0)
+
+
+class TestFileCL(TestCase):
+    def _check_conf(self, config):
+        self.assertEqual(config.a, 10)
+        self.assertEqual(config.b, 20)
+        self.assertEqual(config.Foo.Bar.value, 10)
+        self.assertEqual(config.Foo.Bam.value, list(range(10)))
+        self.assertEqual(config.D.C.value, 'hi there')
+
+    def test_python(self):
+        fd, fname = mkstemp('.py', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write(pyfile)
+        f.close()
+        # Unlink the file
+        cl = PyFileConfigLoader(fname, log=log)
+        config = cl.load_config()
+        self._check_conf(config)
+
+    def test_json(self):
+        fd, fname = mkstemp('.json', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write(json1file)
+        f.close()
+        # Unlink the file
+        cl = JSONFileConfigLoader(fname, log=log)
+        config = cl.load_config()
+        self._check_conf(config)
+
+    def test_context_manager(self):
+
+        fd, fname = mkstemp('.json', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write('{}')
+        f.close()
+
+        cl = JSONFileConfigLoader(fname, log=log)
+
+        value = 'context_manager'
+
+        with cl as c:
+            c.MyAttr.value = value
+
+        self.assertEqual(cl.config.MyAttr.value, value)
+
+        # check that another loader does see the change
+        cl2 = JSONFileConfigLoader(fname, log=log)
+        self.assertEqual(cl.config.MyAttr.value, value)
+
+    def test_json_context_bad_write(self):
+        fd, fname = mkstemp('.json', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write('{}')
+        f.close()
+
+        with JSONFileConfigLoader(fname, log=log) as config:
+            config.A.b = 1
+
+        with self.assertRaises(TypeError):
+            with JSONFileConfigLoader(fname, log=log) as config:
+                config.A.cant_json = lambda x: x
+
+        loader = JSONFileConfigLoader(fname, log=log)
+        cfg = loader.load_config()
+        assert cfg.A.b == 1
+        assert 'cant_json' not in cfg.A
+
+    def test_collision(self):
+        a = Config()
+        b = Config()
+        self.assertEqual(a.collisions(b), {})
+        a.A.trait1 = 1
+        b.A.trait2 = 2
+        self.assertEqual(a.collisions(b), {})
+        b.A.trait1 = 1
+        self.assertEqual(a.collisions(b), {})
+        b.A.trait1 = 0
+        self.assertEqual(a.collisions(b), {
+            'A': {
+                'trait1': "1 ignored, using 0",
+            }
+        })
+        self.assertEqual(b.collisions(a), {
+            'A': {
+                'trait1': "0 ignored, using 1",
+            }
+        })
+        a.A.trait2 = 3
+        self.assertEqual(b.collisions(a), {
+            'A': {
+                'trait1': "0 ignored, using 1",
+                'trait2': "2 ignored, using 3",
+            }
+        })
+
+    def test_v2raise(self):
+        fd, fname = mkstemp('.json', prefix='μnïcø∂e')
+        f = os.fdopen(fd, 'w')
+        f.write(json2file)
+        f.close()
+        # Unlink the file
+        cl = JSONFileConfigLoader(fname, log=log)
+        with self.assertRaises(ValueError):
+            cl.load_config()
+
+
+def _parse_int_or_str(v):
+    try:
+        return int(v)
+    except:
+        return str(v)
+
+
+class MyLoader1(ArgParseConfigLoader):
+    def _add_arguments(self, aliases=None, flags=None, classes=None):
+        p = self.parser
+        p.add_argument('-f', '--foo', dest='Global.foo', type=str)
+        p.add_argument('-b', dest='MyClass.bar', type=int)
+        p.add_argument('-n', dest='n', action='store_true')
+        p.add_argument('Global.bam', type=str)
+        p.add_argument('--list1', action='append', type=_parse_int_or_str)
+        p.add_argument('--list2', nargs='+', type=int)
+
+
+class MyLoader2(ArgParseConfigLoader):
+    def _add_arguments(self, aliases=None, flags=None, classes=None):
+        subparsers = self.parser.add_subparsers(dest='subparser_name')
+        subparser1 = subparsers.add_parser('1')
+        subparser1.add_argument('-x', dest='Global.x')
+        subparser2 = subparsers.add_parser('2')
+        subparser2.add_argument('y')
+
+
+class TestArgParseCL(TestCase):
+
+    def test_basic(self):
+        cl = MyLoader1()
+        config = cl.load_config('-f hi -b 10 -n wow'.split())
+        self.assertEqual(config.Global.foo, 'hi')
+        self.assertEqual(config.MyClass.bar, 10)
+        self.assertEqual(config.n, True)
+        self.assertEqual(config.Global.bam, 'wow')
+        config = cl.load_config(['wow'])
+        self.assertEqual(list(config.keys()), ['Global'])
+        self.assertEqual(list(config.Global.keys()), ['bam'])
+        self.assertEqual(config.Global.bam, 'wow')
+
+    def test_add_arguments(self):
+        cl = MyLoader2()
+        config = cl.load_config('2 frobble'.split())
+        self.assertEqual(config.subparser_name, '2')
+        self.assertEqual(config.y, 'frobble')
+        config = cl.load_config('1 -x frobble'.split())
+        self.assertEqual(config.subparser_name, '1')
+        self.assertEqual(config.Global.x, 'frobble')
+
+    def test_argv(self):
+        cl = MyLoader1(argv='-f hi -b 10 -n wow'.split())
+        config = cl.load_config()
+        self.assertEqual(config.Global.foo, 'hi')
+        self.assertEqual(config.MyClass.bar, 10)
+        self.assertEqual(config.n, True)
+        self.assertEqual(config.Global.bam, 'wow')
+
+    def test_list_args(self):
+        cl = MyLoader1()
+        config = cl.load_config('--list1 1 wow --list2 1 2 3 --list1 B'.split())
+        self.assertEqual(list(config.Global.keys()), ['bam'])
+        self.assertEqual(config.Global.bam, 'wow')
+        self.assertEqual(config.list1, [1, 'B'])
+        self.assertEqual(config.list2, [1, 2, 3])
+
+
+class C(Configurable):
+    str_trait = Unicode(config=True)
+    int_trait = Integer(config=True)
+    list_trait = List(config=True)
+    list_of_ints = List(Integer(), config=True)
+    dict_trait = Dict(config=True)
+    dict_of_ints = Dict(
+        key_trait=Integer(),
+        value_trait=Integer(),
+        config=True,
+    )
+    dict_multi = Dict(
+        key_trait=Unicode(),
+        per_key_traits={
+            "int": Integer(),
+            "str": Unicode(),
+        },
+        config=True,
+    )
+
+
+class TestKeyValueCL(TestCase):
+    klass = KeyValueConfigLoader
+
+    def test_eval(self):
+        cl = self.klass(log=log)
+        config = cl.load_config('--C.str_trait=all --C.int_trait=5 --C.list_trait=["hello",5]'.split())
+        c = C(config=config)
+        assert c.str_trait == 'all'
+        assert c.int_trait == 5
+        assert c.list_trait == ["hello", 5]
+
+    def test_basic(self):
+        cl = self.klass(log=log)
+        argv = [ '--' + s[2:] for s in pyfile.split('\n') if s.startswith('c.') ]
+        config = cl.load_config(argv)
+        assert config.a == '10'
+        assert config.b == '20'
+        assert config.Foo.Bar.value == '10'
+        # non-literal expressions are not evaluated
+        self.assertEqual(config.Foo.Bam.value, 'list(range(10))')
+        self.assertEqual(Unicode().from_string(config.D.C.value), 'hi there')
+
+    def test_expanduser(self):
+        cl = self.klass(log=log)
+        argv = ['--a=~/1/2/3', '--b=~', '--c=~/', '--d="~/"']
+        config = cl.load_config(argv)
+        u = Unicode()
+        self.assertEqual(u.from_string(config.a), os.path.expanduser('~/1/2/3'))
+        self.assertEqual(u.from_string(config.b), os.path.expanduser('~'))
+        self.assertEqual(u.from_string(config.c), os.path.expanduser('~/'))
+        self.assertEqual(u.from_string(config.d), '~/')
+
+    def test_extra_args(self):
+        cl = self.klass(log=log)
+        config = cl.load_config(['--a=5', 'b', 'd', '--c=10'])
+        self.assertEqual(cl.extra_args, ['b', 'd'])
+        assert config.a == '5'
+        assert config.c == '10'
+        config = cl.load_config(['--', '--a=5', '--c=10'])
+        self.assertEqual(cl.extra_args, ['--a=5', '--c=10'])
+
+        cl = self.klass(log=log)
+        config = cl.load_config(['extra', '--a=2', '--c=1', '--', '-'])
+        self.assertEqual(cl.extra_args, ['extra', '-'])
+
+    def test_unicode_args(self):
+        cl = self.klass(log=log)
+        argv = ['--a=épsîlön']
+        config = cl.load_config(argv)
+        print(config, cl.extra_args)
+        self.assertEqual(config.a, 'épsîlön')
+
+    def test_list_append(self):
+        cl = self.klass(log=log)
+        argv = ["--C.list_trait", "x", "--C.list_trait", "y"]
+        config = cl.load_config(argv)
+        assert config.C.list_trait == ["x", "y"]
+        c = C(config=config)
+        assert c.list_trait == ["x", "y"]
+
+    def test_list_single_item(self):
+        cl = self.klass(log=log)
+        argv = ["--C.list_trait", "x"]
+        config = cl.load_config(argv)
+        c = C(config=config)
+        assert c.list_trait == ["x"]
+
+    def test_dict(self):
+        cl = self.klass(log=log)
+        argv = ["--C.dict_trait", "x=5", "--C.dict_trait", "y=10"]
+        config = cl.load_config(argv)
+        c = C(config=config)
+        assert c.dict_trait == {"x": "5", "y": "10"}
+
+    def test_dict_key_traits(self):
+        cl = self.klass(log=log)
+        argv = ["--C.dict_of_ints", "1=2", "--C.dict_of_ints", "3=4"]
+        config = cl.load_config(argv)
+        c = C(config=config)
+        assert c.dict_of_ints == {1: 2, 3: 4}
+
+
+class CBase(Configurable):
+    a = List().tag(config=True)
+    b = List(Integer()).tag(config=True, multiplicity='*')
+    c = List().tag(config=True, multiplicity='append')
+    adict = Dict().tag(config=True)
+
+
+class CSub(CBase):
+    d = Tuple().tag(config=True)
+    e = Tuple().tag(config=True, multiplicity='+')
+    bdict = Dict().tag(config=True, multiplicity='*')
+
+
+class TestArgParseKVCL(TestKeyValueCL):
+    klass = KVArgParseConfigLoader
+
+    def test_no_cast_literals(self):
+        cl = self.klass(log=log)
+        # test ipython -c 1 doesn't cast to int
+        argv = ["-c", "1"]
+        config = cl.load_config(argv, aliases=dict(c="IPython.command_to_run"))
+        assert config.IPython.command_to_run == "1"
+
+    def test_int_literals(self):
+        cl = self.klass(log=log)
+        # test ipython -c 1 doesn't cast to int
+        argv = ["-c", "1"]
+        config = cl.load_config(argv, aliases=dict(c="IPython.command_to_run"))
+        assert config.IPython.command_to_run == "1"
+
+    def test_unicode_alias(self):
+        cl = self.klass(log=log)
+        argv = ['--a=épsîlön']
+        config = cl.load_config(argv, aliases=dict(a='A.a'))
+        print(dict(config))
+        print(cl.extra_args)
+        print(cl.aliases)
+        self.assertEqual(config.A.a, 'épsîlön')
+
+    def test_expanduser2(self):
+        cl = self.klass(log=log)
+        argv = ['-a', '~/1/2/3', '--b', "'~/1/2/3'"]
+        config = cl.load_config(argv, aliases=dict(a='A.a', b='A.b'))
+
+        class A(Configurable):
+            a = Unicode(config=True)
+            b = Unicode(config=True)
+
+        a = A(config=config)
+        self.assertEqual(a.a, os.path.expanduser('~/1/2/3'))
+        self.assertEqual(a.b, '~/1/2/3')
+
+    def test_eval(self):
+        cl = self.klass(log=log)
+        argv = ['-c', 'a=5']
+        config = cl.load_config(argv, aliases=dict(c='A.c'))
+        self.assertEqual(config.A.c, "a=5")
+
+    def test_seq_traits(self):
+        cl = self.klass(log=log, classes=(CBase, CSub))
+        aliases = {'a3': 'CBase.c', 'a5': 'CSub.e'}
+        argv = ("--CBase.a A --CBase.a 2 --CBase.b 1 --CBase.b 3 --a3 AA --CBase.c BB "
+                "--CSub.d 1 --CSub.d BBB --CSub.e 1 --CSub.e=bcd a b c ").split()
+        config = cl.load_config(argv, aliases=aliases)
+        assert cl.extra_args == ["a", "b", "c"]
+        assert config.CBase.a == ['A', '2']
+        assert config.CBase.b == [1, 3]
+        self.assertEqual(config.CBase.c, ['AA', 'BB'])
+
+        assert config.CSub.d == ('1', 'BBB')
+        assert config.CSub.e == ('1', 'bcd')
+
+    def test_seq_traits_single_empty_string(self):
+        cl = self.klass(log=log, classes=(CBase, ))
+        aliases = {'seqopt': 'CBase.c'}
+        argv = ['--seqopt', '']
+        config = cl.load_config(argv, aliases=aliases)
+        self.assertEqual(config.CBase.c, [''])
+
+    def test_dict_traits(self):
+        cl = self.klass(log=log, classes=(CBase, CSub))
+        aliases = {'D': 'CBase.adict', 'E': 'CSub.bdict'}
+        argv = ["-D", "k1=v1", "-D=k2=2", "-D", "k3=v 3", "-E", "k=v", "-E", "22=222"]
+        config = cl.load_config(argv, aliases=aliases)
+        c = CSub(config=config)
+        assert c.adict == {'k1': 'v1', 'k2': '2', 'k3': 'v 3'}
+        assert c.bdict == {'k': 'v', '22': '222'}
+
+    def test_mixed_seq_positional(self):
+        aliases = {"c": "Class.trait"}
+        cl = self.klass(log=log, aliases=aliases)
+        assignments = [("-c", "1"), ("--Class.trait=2",), ("--c=3",), ("--Class.trait", "4")]
+        positionals = ["a", "b", "c"]
+        # test with positionals at any index
+        for idx in range(len(assignments) + 1):
+            argv_parts = assignments[:]
+            argv_parts[idx:idx] = (positionals,)
+            argv = list(chain(*argv_parts))
+
+            config = cl.load_config(argv)
+            assert config.Class.trait == ["1", "2", "3", "4"]
+            assert cl.extra_args == ["a", "b", "c"]
+
+    def test_split_positional(self):
+        """Splitting positionals across flags is no longer allowed in traitlets 5"""
+        cl = self.klass(log=log)
+        argv = ["a", "--Class.trait=5", "b"]
+        with pytest.raises(SystemExit):
+            cl.load_config(argv)
+
+
+class TestConfig(TestCase):
+
+    def test_setget(self):
+        c = Config()
+        c.a = 10
+        self.assertEqual(c.a, 10)
+        self.assertEqual('b' in c, False)
+
+    def test_auto_section(self):
+        c = Config()
+        self.assertNotIn('A', c)
+        assert not c._has_section('A')
+        A = c.A
+        A.foo = 'hi there'
+        self.assertIn('A', c)
+        assert c._has_section('A')
+        self.assertEqual(c.A.foo, 'hi there')
+        del c.A
+        self.assertEqual(c.A, Config())
+
+    def test_merge_doesnt_exist(self):
+        c1 = Config()
+        c2 = Config()
+        c2.bar = 10
+        c2.Foo.bar = 10
+        c1.merge(c2)
+        self.assertEqual(c1.Foo.bar, 10)
+        self.assertEqual(c1.bar, 10)
+        c2.Bar.bar = 10
+        c1.merge(c2)
+        self.assertEqual(c1.Bar.bar, 10)
+
+    def test_merge_exists(self):
+        c1 = Config()
+        c2 = Config()
+        c1.Foo.bar = 10
+        c1.Foo.bam = 30
+        c2.Foo.bar = 20
+        c2.Foo.wow = 40
+        c1.merge(c2)
+        self.assertEqual(c1.Foo.bam, 30)
+        self.assertEqual(c1.Foo.bar, 20)
+        self.assertEqual(c1.Foo.wow, 40)
+        c2.Foo.Bam.bam = 10
+        c1.merge(c2)
+        self.assertEqual(c1.Foo.Bam.bam, 10)
+
+    def test_deepcopy(self):
+        c1 = Config()
+        c1.Foo.bar = 10
+        c1.Foo.bam = 30
+        c1.a = 'asdf'
+        c1.b = range(10)
+        c1.Test.logger = logging.Logger('test')
+        c1.Test.get_logger = logging.getLogger('test')
+        c2 = copy.deepcopy(c1)
+        self.assertEqual(c1, c2)
+        self.assertTrue(c1 is not c2)
+        self.assertTrue(c1.Foo is not c2.Foo)
+        self.assertTrue(c1.Test is not c2.Test)
+        self.assertTrue(c1.Test.logger is c2.Test.logger)
+        self.assertTrue(c1.Test.get_logger is c2.Test.get_logger)
+
+    def test_builtin(self):
+        c1 = Config()
+        c1.format = "json"
+
+    def test_fromdict(self):
+        c1 = Config({'Foo' : {'bar' : 1}})
+        self.assertEqual(c1.Foo.__class__, Config)
+        self.assertEqual(c1.Foo.bar, 1)
+
+    def test_fromdictmerge(self):
+        c1 = Config()
+        c2 = Config({'Foo' : {'bar' : 1}})
+        c1.merge(c2)
+        self.assertEqual(c1.Foo.__class__, Config)
+        self.assertEqual(c1.Foo.bar, 1)
+
+    def test_fromdictmerge2(self):
+        c1 = Config({'Foo' : {'baz' : 2}})
+        c2 = Config({'Foo' : {'bar' : 1}})
+        c1.merge(c2)
+        self.assertEqual(c1.Foo.__class__, Config)
+        self.assertEqual(c1.Foo.bar, 1)
+        self.assertEqual(c1.Foo.baz, 2)
+        self.assertNotIn('baz', c2.Foo)
+
+    def test_contains(self):
+        c1 = Config({'Foo' : {'baz' : 2}})
+        c2 = Config({'Foo' : {'bar' : 1}})
+        self.assertIn('Foo', c1)
+        self.assertIn('Foo.baz', c1)
+        self.assertIn('Foo.bar', c2)
+        self.assertNotIn('Foo.bar', c1)
+
+    def test_pickle_config(self):
+        cfg = Config()
+        cfg.Foo.bar = 1
+        pcfg = pickle.dumps(cfg)
+        cfg2 = pickle.loads(pcfg)
+        self.assertEqual(cfg2, cfg)
+
+    def test_getattr_section(self):
+        cfg = Config()
+        self.assertNotIn('Foo', cfg)
+        Foo = cfg.Foo
+        assert isinstance(Foo, Config)
+        self.assertIn('Foo', cfg)
+
+    def test_getitem_section(self):
+        cfg = Config()
+        self.assertNotIn('Foo', cfg)
+        Foo = cfg['Foo']
+        assert isinstance(Foo, Config)
+        self.assertIn('Foo', cfg)
+
+    def test_getattr_not_section(self):
+        cfg = Config()
+        self.assertNotIn('foo', cfg)
+        foo = cfg.foo
+        assert isinstance(foo, LazyConfigValue)
+        self.assertIn('foo', cfg)
+
+    def test_getattr_private_missing(self):
+        cfg = Config()
+        self.assertNotIn('_repr_html_', cfg)
+        with self.assertRaises(AttributeError):
+            _ = cfg._repr_html_
+        self.assertNotIn('_repr_html_', cfg)
+        self.assertEqual(len(cfg), 0)
+
+    def test_lazy_config_repr(self):
+        cfg = Config()
+        cfg.Class.lazy.append(1)
+        cfg_repr = repr(cfg)
+        assert '<LazyConfigValue' in cfg_repr
+        assert "extend" in cfg_repr
+        assert " [1]}>" in cfg_repr
+        assert 'value=' not in cfg_repr
+        cfg.Class.lazy.get_value([0])
+        repr2 = repr(cfg)
+        assert repr([0,1]) in repr2
+        assert 'value=' in repr2
+
+
+    def test_getitem_not_section(self):
+        cfg = Config()
+        self.assertNotIn('foo', cfg)
+        foo = cfg['foo']
+        assert isinstance(foo, LazyConfigValue)
+        self.assertIn('foo', cfg)
+
+    def test_merge_no_copies(self):
+        c = Config()
+        c2 = Config()
+        c2.Foo.trait = []
+        c.merge(c2)
+        c2.Foo.trait.append(1)
+        self.assertIs(c.Foo, c2.Foo)
+        self.assertEqual(c.Foo.trait, [1])
+        self.assertEqual(c2.Foo.trait, [1])
+
+    
+    def test_merge_multi_lazy(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        If systemwide overwirte and user append, we want both in the right
+        order.
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait = [1]
+        c2.Foo.trait.append(2)
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait, [1,2] )
+
+
+    
+    def test_merge_multi_lazyII(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        If both are lazy we still want a lazy config.
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait.append(1)
+        c2.Foo.trait.append(2)
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait._extend, [1,2] )
+
+    def test_merge_multi_lazy_III(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        Prepend should prepend in the right order.
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait = [1]
+        c2.Foo.trait.prepend([0])
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait, [0, 1] )
+
+    def test_merge_multi_lazy_IV(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        Both prepending should be lazy
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait.prepend([1])
+        c2.Foo.trait.prepend([0])
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait._prepend, [0, 1])
+
+    def test_merge_multi_lazy_update_I(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        dict update shoudl be in the right order.
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait = {"a": 1, "z": 26}
+        c2.Foo.trait.update({"a": 0, "b": 1})
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait, {"a": 0, "b": 1, "z": 26})
+
+    def test_merge_multi_lazy_update_II(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        Later dict overwrite lazyness
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait.update({"a": 0, "b": 1})
+        c2.Foo.trait = {"a": 1, "z": 26}
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait, {"a": 1, "z": 26})
+
+    def test_merge_multi_lazy_update_III(self):
+        """
+        With multiple config files (systemwide and users), we want compounding.
+
+        Later dict overwrite lazyness
+        """
+        c1 = Config()
+        c2 = Config()
+
+        c1.Foo.trait.update({"a": 0, "b": 1})
+        c2.Foo.trait.update({"a": 1, "z": 26})
+
+        c = Config()
+        c.merge(c1)
+        c.merge(c2)
+
+        self.assertEqual(c.Foo.trait._update, {"a": 1, "z": 26, "b": 1})