Traitlets

- Fix casting bytes to unicode

a period of more close to four years; A number of internal refactoring
made the internal code structure cleaner and simpler, and greatly
improved the diagnostic error messages as well has help and
documentation generation.

We expect no code change needed for any consumer of the Python API
(ipywidgets, and alike), though CLI argument parsing have seen a
complete rewrite, so if you have an application that does use the
parsing logic of traitlets you may see changes in behavior, and now have
access to more features. There was also a cleanup of what was considered
a part of the public API, certain previously exposed utility functions
and types are no longer available. Please see an exhaustive list below.

::: seealso
`commandline` docs for details about
command-line parsing and the changes in 5.0.

Please [let us know](https://github.com/ipython/traitlets/issues) if you
find issues with the new command-line parsing changes.
:::

We also want to thanks in particular a number of regular contributor
through the years that have patiently waited for their often large
contribution to be available, if **rough** order of number of
contribution:

- Ryan Morshead - rmorshea - For serving as a maintainer of the
4.x branch and providing a number of bug fix through the years.
- Kostis Anagnostopoulos - ankostis - Who push a major refactor of
the CLI paring, as well as many help-generating function.
- Benjamin Ragan-Kelley -- minrk -- for reviewing and help fixing
edge case in most of the above
- Matthias Bussonnier -- carreau
- Sylvain Corlay
- Francisco de la Peña
- Martin Renou
- Yves Delley
- Thomas Kluyver
- hristian Clauss
- maartenbreddels
- Aliaksei Urbanski
- Kevin Bates
- David Brochart

As well as many of the passer-by, and less frequent contributors:

- Tim Paine
- Jake VanderPlas
- Frédéric Chapoton
- Dan Allan
- Adam Chainz
- William Krinsman
- Travis DePrato
- Todd
- Thomas Aarholt
- Lumir Balhar
- Leonardo Uieda
- Leo Gallucci
- Kyle Kelley
- Jeroen Demeyer
- Jason Grout
- Hans Moritz Günther
- FredInChina
- Conner Cowling
- Carol Willing
- Albert Zeyer

Major changes are:

- Removal of Python 2 support,
- Removal of Python 3.0-3.6 support
- we now follow NEP 29, and are thus Python 3.7+ only.
- remove `six` as a dependency
- remove `funcsig` as a dependency.
- no longer exposes the following functions / types:
- ClassTypes
- DefaultHandler
- EventHandler
- ForwardDeclaredMixin
- ObserveHandler
- SequenceTypes
- ValidateHandler
- add_article
- class_of
- getargspec
- getmembers
- is_trait
- isidentifier
- repr_type

Here is a list of most Pull requests that went into 5.0 and a short
description.

- [362](https://github.com/ipython/traitlets/pull/362) , [#361](https://github.com/ipython/traitlets/pull/361) introduces:
- help for aliases , aliases dict values can now be a tuple with
('target', 'help string')
- subcommands can now be arbitrary callable and do not need to be
subclass of `Application`
- [306](https://github.com/ipython/traitlets/pull/306) Add compatibility with the
`trait` package for Dictionaries and add the `key_trait` parameters
allowing to restrict the type of the key of a mapping. The
constructor parameters `trait` and `traits` are renamed to
`value_trait` and `per_key_traits`.
- [319](https://github.com/ipython/traitlets/pull/319) adds ability to introduce
both shot and long version of aliases, allowing for short and long
options `-` and `--`.
- [322](https://github.com/ipython/traitlets/pull/322) rewrite command line argument
parsing to use argparse, and allow more flexibility in assigning
literals without quoting.
- [332](https://github.com/ipython/traitlets/pull/332) Make it easier to redefined
default values of parents classes.
- [333](https://github.com/ipython/traitlets/pull/333) introduces a
`Callable` trait.
- [340](https://github.com/ipython/traitlets/pull/340) Old way of passing containers
in the command line is now deprecated, and will emit warning on the
command line.
- [341](https://github.com/ipython/traitlets/pull/341) introduces
`--Application.show_config=True` which will make by default any
application show it configuration, all the files it loaded
configuration from, and exit.
- [349](https://github.com/ipython/traitlets/pull/349) unify ability to declare
default values across traitlets with a singular method `default`
method, and [525](https://github.com/ipython/traitlets/pull/525) adds a warning
that `Undefined`is deprecated.
- [355](https://github.com/ipython/traitlets/pull/355) fix a random ordering issues
in command lines flags.
- [356](https://github.com/ipython/traitlets/pull/356) allow both `self` and `cls`
in `__new__` method for genericity.
- [360](https://github.com/ipython/traitlets/pull/360) Simplify overwriting and
extending the command line argument parser.
- [371](https://github.com/ipython/traitlets/pull/371) introduces a
`FuzzyEnum` trait that allow case
insensitive and unique prefix matching.
- [384](https://github.com/ipython/traitlets/pull/384) Ass a
`trait_values` method to extra a mapping of trait and
their values.
- [393](https://github.com/ipython/traitlets/pull/393) `Link` now have a
transform attribute (taking two functions inverse of each other),
that affect how a value is mapped between a source and a target.
- [394](https://github.com/ipython/traitlets/pull/394) `Link` now have a
`link` method to re-link object after
`unlink` has been called.
- [402](https://github.com/ipython/traitlets/pull/402) rewrite handling of error
messages for nested traits.
- [405](https://github.com/ipython/traitlets/pull/405) all function that use to
print help now have an equivalent that yields the help lines.
- [413](https://github.com/ipython/traitlets/pull/413) traits now have a method
`trait_has_value`, returning a boolean to know if a
value has been assigned to a trait (excluding the default), in order
to help avoiding circular validation at initialisation.
- [416](https://github.com/ipython/traitlets/pull/416) Explicitly export traitlets
in `__all__` to avoid exposing implementation details.
- [438](https://github.com/ipython/traitlets/pull/438) introduces `.info_rst()` to
let traitlets overwrite the automatically generated rst
documentation.
- [458](https://github.com/ipython/traitlets/pull/458) Add a sphinx extension to
automatically document options of `Application` instance
in projects using traitlets.
- [509](https://github.com/ipython/traitlets/pull/509) remove all base `except:`
meaning traitlets will not catch a number of
`BaseException` s anymore.
- [515](https://github.com/ipython/traitlets/pull/515) Add a class decorator to
enable tab completion of keyword arguments in signature.
- [516](https://github.com/ipython/traitlets/pull/516) a `Sentinel` Traitlets was
made public by mistake and is now deprecated.
- [517](https://github.com/ipython/traitlets/pull/517) use parent Logger within
logggin configurable when possible.
- [522](https://github.com/ipython/traitlets/pull/522) Make loading config files
idempotent and expose the list of loaded config files for long
running services.

API changes

This list is auto-generated by `frappuccino`, comparing with traitlets

(This is an in-progress changelog, please let us know if something is
missing/or could be phrased better)

The following items are new:
+ traitlets.Sentinel
+ traitlets.config.application.Application.emit_alias_help(self)
+ traitlets.config.application.Application.emit_description(self)
+ traitlets.config.application.Application.emit_examples(self)
+ traitlets.config.application.Application.emit_flag_help(self)
+ traitlets.config.application.Application.emit_help(self, classes=False)
+ traitlets.config.application.Application.emit_help_epilogue(self, classes)
+ traitlets.config.application.Application.emit_options_help(self)
+ traitlets.config.application.Application.emit_subcommands_help(self)
+ traitlets.config.application.Application.start_show_config(self)
+ traitlets.config.application.default_aliases
+ traitlets.config.application.default_flags
+ traitlets.config.default_aliases
+ traitlets.config.default_flags
+ traitlets.config.loader.DeferredConfig
+ traitlets.config.loader.DeferredConfig.get_value(self, trait)
+ traitlets.config.loader.DeferredConfigList
+ traitlets.config.loader.DeferredConfigList.get_value(self, trait)
+ traitlets.config.loader.DeferredConfigString
+ traitlets.config.loader.DeferredConfigString.get_value(self, trait)
+ traitlets.config.loader.LazyConfigValue.merge_into(self, other)
+ traitlets.config.loader.Undefined
+ traitlets.config.loader.class_trait_opt_pattern
+ traitlets.traitlets.BaseDescriptor.subclass_init(self, cls)
+ traitlets.traitlets.Bool.from_string(self, s)
+ traitlets.traitlets.Bytes.from_string(self, s)
+ traitlets.traitlets.Callable
+ traitlets.traitlets.Callable.validate(self, obj, value)
+ traitlets.traitlets.CaselessStrEnum.info(self)
+ traitlets.traitlets.CaselessStrEnum.info_rst(self)
+ traitlets.traitlets.Complex.from_string(self, s)
+ traitlets.traitlets.Container.from_string(self, s)
+ traitlets.traitlets.Container.from_string_list(self, s_list)
+ traitlets.traitlets.Container.item_from_string(self, s)
+ traitlets.traitlets.Dict.from_string(self, s)
+ traitlets.traitlets.Dict.from_string_list(self, s_list)
+ traitlets.traitlets.Dict.item_from_string(self, s)
+ traitlets.traitlets.Enum.from_string(self, s)
+ traitlets.traitlets.Enum.info_rst(self)
+ traitlets.traitlets.Float.from_string(self, s)
+ traitlets.traitlets.FuzzyEnum
+ traitlets.traitlets.FuzzyEnum.info(self)
+ traitlets.traitlets.FuzzyEnum.info_rst(self)
+ traitlets.traitlets.FuzzyEnum.validate(self, obj, value)
+ traitlets.traitlets.HasTraits.trait_defaults(self, *names, **metadata)
+ traitlets.traitlets.HasTraits.trait_has_value(self, name)
+ traitlets.traitlets.HasTraits.trait_values(self, **metadata)
+ traitlets.traitlets.Instance.from_string(self, s)
+ traitlets.traitlets.Int.from_string(self, s)
+ traitlets.traitlets.ObjectName.from_string(self, s)
+ traitlets.traitlets.TCPAddress.from_string(self, s)
+ traitlets.traitlets.TraitType.default(self, obj='None')
+ traitlets.traitlets.TraitType.from_string(self, s)
+ traitlets.traitlets.Unicode.from_string(self, s)
+ traitlets.traitlets.Union.default(self, obj='None')
+ traitlets.traitlets.UseEnum.info_rst(self)
+ traitlets.traitlets.directional_link.link(self)
+ traitlets.traitlets.link.link(self)
+ traitlets.utils.cast_unicode(s, encoding='None')
+ traitlets.utils.decorators
+ traitlets.utils.decorators.Undefined
+ traitlets.utils.decorators.signature_has_traits(cls)
+ traitlets.utils.descriptions
+ traitlets.utils.descriptions.add_article(name, definite=False, capital=False)
+ traitlets.utils.descriptions.class_of(value)
+ traitlets.utils.descriptions.describe(article, value, name='None', verbose=False, capital=False)
+ traitlets.utils.descriptions.repr_type(obj)

The following items have been removed (or moved to superclass):
- traitlets.ClassTypes
- traitlets.SequenceTypes
- traitlets.config.absolute_import
- traitlets.config.application.print_function
- traitlets.config.configurable.absolute_import
- traitlets.config.configurable.print_function
- traitlets.config.loader.KeyValueConfigLoader.clear
- traitlets.config.loader.KeyValueConfigLoader.load_config
- traitlets.config.loader.flag_pattern
- traitlets.config.loader.kv_pattern
- traitlets.config.print_function
- traitlets.traitlets.ClassBasedTraitType.error
- traitlets.traitlets.Container.element_error
- traitlets.traitlets.List.validate
- traitlets.traitlets.TraitType.instance_init
- traitlets.traitlets.Union.make_dynamic_default
- traitlets.traitlets.add_article
- traitlets.traitlets.class_of
- traitlets.traitlets.repr_type
- traitlets.utils.getargspec.PY3
- traitlets.utils.importstring.string_types
- traitlets.warn_explicit

The following signatures differ between versions:

- traitlets.config.application.Application.generate_config_file(self)
+ traitlets.config.application.Application.generate_config_file(self, classes='None')

- traitlets.config.application.catch_config_error(method, app, *args, **kwargs)
+ traitlets.config.application.catch_config_error(method)

- traitlets.config.configurable.Configurable.class_config_section()
+ traitlets.config.configurable.Configurable.class_config_section(classes='None')

- traitlets.config.configurable.Configurable.class_get_trait_help(trait, inst='None')
+ traitlets.config.configurable.Configurable.class_get_trait_help(trait, inst='None', helptext='None')

- traitlets.config.loader.ArgParseConfigLoader.load_config(self, argv='None', aliases='None', flags='None')
+ traitlets.config.loader.ArgParseConfigLoader.load_config(self, argv='None', aliases='None', flags='<deprecated>', classes='None')

- traitlets.traitlets.Dict.element_error(self, obj, element, validator)
+ traitlets.traitlets.Dict.element_error(self, obj, element, validator, side='Values')

- traitlets.traitlets.HasDescriptors.setup_instance(self, *args, **kwargs)
+ traitlets.traitlets.HasDescriptors.setup_instance(*args, **kwargs)

- traitlets.traitlets.HasTraits.setup_instance(self, *args, **kwargs)
+ traitlets.traitlets.HasTraits.setup_instance(*args, **kwargs)

- traitlets.traitlets.TraitType.error(self, obj, value)
+ traitlets.traitlets.TraitType.error(self, obj, value, error='None', info='None')

- Compatibility fix for Python 3.6a1
- Fix bug in Application.classes getting extra entries when multiple
Applications are instantiated in the same process.