Traits 6.4.3

This is a bugfix release that fixes test failures with Sphinx 7.2 and later,
and adds support for Python 3.12.

Fixes

• Use pathlib.Path instead of sphinx.testing.path.path for Sphinx
  7.2 and later. (#1755)
• Fix uses of the deprecated datetime.utcnow method. (#1758)
• Update CI and workflows for Python 3.12 support. (#1757)

Traits 6.4.2

This is a bugfix release that fixes some test failures with the
most recent TraitsUI versions.

Fixes

• Replace a deprecated version check for TraitsUI. (#1746)
• Fix a test that fails on warnings other than those directly
  related to the test purpose. (#1749)

Traits 6.4.1

This is a bugfix release that fixes wheel builds on Python 3.11 and
fixes some distribution and testing issues with typing stubs.

Fixes

* Update `cibuildwheel` to the latest version so that we get wheels for
  Python 3.11. (#1711)
* Rename `requires_numpy_testing` decorator to `requires_numpy_typing`,
  and have it check for `numpy.typing`, not `numpy.testing`. (#1710)
* Fix missing `numpy_examples` directory in traits-stubs package data.
  (#1709)

Traits 6.4.0

Traits 6.4 is a minor feature release of Traits, which focuses mainly on typing
stub and documentation updates.

Migrating from Traits 6.3

Traits 6.4 should be largely backwards compatible with Traits 6.3, but there
are a couple of things to watch out for.

• Reminder: while the Either and Trait trait types are not yet formally
  deprecated, the intention is to eventually deprecate and remove them.
  Projects are encouraged to update their code to use Union instead.
• Similarly, any uses of the Unicode trait type in your project should
  be replaced with Str.
• Validation of items within a container (e.g., foos = List(MyTraitType))
  now always matches the validation used for the item trait at top level (e.g.,
  foo = MyTraitType). Previously, the validation methods used could differ,
  thanks to a bug in the container implementations. For most trait types this
  will make no difference, but for the Tuple trait type this change has the
  consequence that lists will no longer be accepted as valid for Tuple
  traits inside list items. See issue #1619 and PR #1625 for more information.
• Related to the above: a top-level Tuple() trait declaration currently
  accepts Python list objects, while a Tuple declaration with explicit
  item types (for example Tuple(Int(), Int())) does not. The support for
  list objects in plain Tuple() is deprecated, and will be removed in a
  future version of Traits. See PR #1627 for more information.

Detailed PR-by-PR changes

The following people contributed code changes for this release:

• Caio Agiani
• Steve Allen
• Mark Dickinson
• Sai Rahul Poruri
• Corran Webster

Features

• ETSConfig attributes now support deletion. This makes it easier to make
  temporary changes to ETSConfig attributes during unit testing. (#1670,
  #1686)
• Complex trait type validation is now more lenient: any type that
  implements __complex__ will be accepted. (#1594)
• BaseFloat validation is now more lenient, and matches Float
  validation: BaseFloat now also accepts objects whose type has an
  __index__ method. (#1595)

Changes

• An enumerate alias has been removed from traits.trait_base. In the
  unlikely event of code that imports enumerate from traits.trait_base,
  use the built-in enumerate instead. (#1681)
• Fast validation tuples int_fast_validate, float_fast_validate and
  complex_fast_validate have been removed from the traits.trait_types
  module. (#1601)

Fixes

• TraitListObject, TraitDict object and TraitSetObject now use the
  validate method of the appropriate CTrait instances to validate
  items, keys and values. Previously the handler's validate method was
  used; this gave buggy behaviour in cases where the handler's validate
  method differed from the actual validation in use. (#1625)
• Fix specification of default_value that incorrectly disregarded
  default_value_type. (#1631)
• Fix incorrect results from clone_traits applied to List, Dict
  and Set traits. (#1624)
• The find_resource and store_resource tests are now skipped
  if the pkg_resources module is not present in the environment. (#1679)
• An ETSConfig test has been renamed so that it's properly picked up
  by the test runner. (#1671)
• Fix some ETSConfig tests that assume unittest as the test runner. (#1683)
• Rename various test-related classes to avoid pytest trying to harvest test
  methods from them. (#1684)
• Overriding a default for a List or other collection trait in a subclass
  now works as expected. Previously, the behaviour was unusably buggy. (#1645)

Deprecations

• Tuple traits currently accept Python list objects in some (but
  not all) circumstances. That feature is deprecated, and will be removed
  in a future version of Traits. (#1627)

Type stubs

• Add stubs for Array, ArrayOrNone, and CArray. (#1682)
• Fix various stubs for traits.trait_types; add stubs for
  traits.ctraits. (#1661)
• Fix that TraitError stubs weren't exposed at traits.api level.
  (#1658)
• Make Int and Float type stubs more accurate. (#1656)
• Fix incorrect type stubs for the Dict trait type. (#1655)

Documentation

• Make ETSConfig class documentation visible in the API docs. (#1688)
• Add copy buttons to code samples in documentation. (#1651, #1653)
• Document Date, Datetime and Time trait types. (#1641)
• Fix some missing mentions of Set in notification docs. (#1618)
• Document the 'some_trait.-' pattern for on_trait_change. (#1592)
• Document that Either should not be used in new code. (#1699)
• Document that TraitPrefixMap and TraitPrefixList are deprecated.
  (#1702)
• Document that the Trait factory function should not be used in new code.
  (#1700)
• Miscellaneous minor fixes. (#1583, #1611, #1652, #1680)

Build and continuous integration

• Don't collect traits-stubs tests under pytest. As a result of this
  and other fixes, the test suite now passes under pytest. (#1690)
• Update etstool.py for Python 3.8 support. Python 3.8 is now the
  default Python version for builds. (#1694)
• Use PySide6 for Python >= 3.8 instead of PySide2 in CI testing. (#1685)
• Add pyproject.toml files for both Traits and traits-stubs. (#1689, #1676)
• Add Python 3.11 to some workflow runs. (#1600, #1660, #1674)
• Add Python 3.10 to install-from-PyPI workflow. (#1576)
• Allow running the main test workflow manually. (#1607)
• Switch Slack channel used to report GitHub Actions failures. (#1650)
• Exclude build directory in flake8 configuration. (#1635)
• Re-include NumPy as a test dependency on Python 3.10. (#1593)

Maintenance and refactoring

• .gitignore cleanup and updates. (#1678, #1687)
• Return PyErr_Format calls in traits/ctraits.c. (#1640)
• Update copyright header end year to 2022. (#1612)
• The ci-src-requirements.txt file isn't used; remove it. (#1602)

Traits 6.3.2

Traits 6.3.2 is a bugfix release, fixing an issue with duplicate
notifications from Property traits using the observe framework.

Fixes

• Fix that Property traits using observe metadata could be fired
  twice in subclasses. (#1587)

Traits 6.3.1

Traits 6.3.1 is a bugfix release, fixing an incompatibility between Traits 6.3.0 and Mayavi <= 4.7.3.

Fixes

• Make PrefixMap._map available again, for compatibility with Mayavi.
  (#1578)

Traits 6.3.0

Traits 6.3 is the latest feature release in the Traits 6 series, with several
improvements and fixes over Traits 6.2.

Highlights of this release

• There have been various minor performance improvements to the core
  on_trait_change and observe machinery. These may improve
  startup time for some Traits-using applications.
• The observe mini-language now has in-language support for listening
  to all traits, using the * character.
• Support for Python 3.10 has been added.

Migration guide

Traits 6.3 is intended to be fully backwards compatible with Traits 6.2, and
most projects should have no difficulties upgrading. However, you may see
some new deprecation warnings for existing code, warning about behaviour
that will be changed in Traits 7.0. There are two particular sets of changes
to look out for:

• Starting with Traits 7.0, the Any trait type will treat a default
  value of type list or dict differently. Currently, instances of
  list and dict are special-cased, and a per-instance copy of the
  default is provided to each HasTraits instance. In Traits 7.0, this
  special-casing will be removed, and the default value will be shared between
  all instances. For the 6.3 release of Traits, a deprecation warning is issued
  whenever a trait definition of the form Any([1, 2, 3]) or Any({})
  is encountered. Users can retain the existing behaviour and suppress the
  warning by changing their code to use the new factory argument to the
  Any trait type, for example replacing a trait declaration foo = Any({}) with foo = Any(factory=dict), and a trait declaration foo = Any([1, 2, 3]) with foo = Any(factory=list, args=([1, 2, 3],)).

• Starting with Traits 7.0, the Date trait type will no longer accept
  datetime instances by default. Traits 6.3 will issue a deprecation
  warning whenever a datetime instance is assigned as a value for
  a Date trait. The existing behaviour can be preserved and the warning
  silenced by using Date(allow_datetime=True); alternatively, you can
  use Date(allow_datetime=False) to adopt the Traits 7.0 behaviour
  right now.

Detailed PR-by-PR changes

Over 80 pull requests went into this release. The following people contributed
to the release:

• @0xflotus
• Aaron Ayres
• Kit Choi
• Mark Dickinson
• Chigozie Nri
• Poruri Sai Rahul
• Corran Webster
• John Wiggins
• Peter Zahemszky

Thank you to all who contributed!

Features

• The observe mini-language now supports use of "*" for listening to
  all traits on a HasTraits object. Currently this support is limited to
  cases where the "*" appears in a terminal position. For example,
  observe("foo:*") is supported, but observe("*:foo") is not.
  (#1496, #1525)
• The Any trait type now supports a factory argument (with accompanying
  args and kw arguments). This can be used to specify a per-instance
  default, for example with Any(factory=dict). (#1557, #1558)
• The DefaultValue enumeration has a new member DefaultValue.disallow
  intended to be used for trait types that don't have a meaningful default. For
  traits using this default value type, an attempt to retrieve the
  corresponding default using default_value_for will raise ValueError.
  (#1546)
• When a method is decorated with an observe decorator, the method
  signature is now checked, and a warning issued if it doesn't match the
  expected signature. This should catch the common error of forgetting to
  provide the event parameter. (#1529)
• In ETSToolkit, the "qt" toolkit name is now supported as a synonym
  for "qt4". (#1436)
• The Date, Datetime and Time trait types have a new argument
  allow_none. In the future, these trait types will not accept None
  unless allow_none=True is specified. (#1432)
• The Date trait type has a new argument allow_datetime. In the future,
  datetime instances will not be valid values for a Date trait unless
  allow_datetime=True is specified. (#1429)

Performance

• The ObserverGraph instances that result from compiling
  ObserverExpression objects and observe mini-language strings are now
  cached. This should speed up creation and instantiation of HasTraits
  subclasses that involve listening for the same pattern in multiple places.
  (#1516, #1528)
• The equality definition on ObserverExpression has been simplified.
  (#1517)
• The ObserverExpression, ObserverGraph and related
  classes now use __slots__ to improve speed and memory use. (#1513, #1515)
• The on_trait_change method has been sped up by almost a factor of two,
  by removing unnecessary internal usage of Traits in the parsing and listener
  functionality. (#1490, #1491, #1492, #1493)

Changes

• An invalid static default value in a PrefixList or PrefixMap trait
  declaration now raises ValueError rather than TraitError. (#1564)
• PrefixList and PrefixMap no longer cache completions. (#1564)
• A failure to parse an observe mini-language string now raises
  ValueError rather than LarkError. (#1507)
• The NotifierNotFound exception is now published in
  traits.observation.api. (#1498)
• An attempt to access a nonexistent "dunder" attribute (an attribute whose
  name starts and ends with "__") on a CTrait instance will now raise
  AttributeError. Previously, it would return None. (#1469, #1474,
  #1477)

Deprecations

• The Any trait type currently implicitly makes a per-HasTraits-instance
  copy of the default value if that value is an instance of either list or
  dict. This behaviour is deprecated, and will be removed in Traits 7.0.
  For a per-instance default, use the new factory argument to Any
  instead. (#1548, #1532)
• The Date, Datetime and Time trait types will no longer accept
  None as a valid trait value in the future. To keep the existing
  behaviour, use the new allow_none keyword argument to these trait types.
  (#1444)
• The Date trait type will no longer accept datetime instances by
  default in the future. To keep the existing behaviour, use the new
  allow_datetime keyword argument. (#1441)
• The Symbol trait type is deprecated. For resolution of a string
  representing a package/module/object combination, use import_symbol
  instead. (#1542)
• The MetaHasTraits.add_listener and MetaHasTraits.remove_listener
  methods are deprecated. (#1550)
• The clean_filename and clean_timestamp utilities are deprecated. If
  you need these utilities in your own project, you're advised to copy the
  code directly into your project. (#1527)
• The find_resource and store_resource functions are deprecated. New
  code should use importlib.resources or importlib_resources instead
  of either of these functions. (#1501)

Fixes

• Invalid assignments to PrefixList and PrefixMap traits produced
  an unnecessarily nested exception. This has been fixed. (#1564)
• An observe-decorated listener method whose name has the special form
  "_traitname_changed" will no longer be triggered both as as result
  of the observe decorator and the special naming: it will only be
  triggered via the observe decorator. (#1560)
• The delegate parameter was mistyped in the typing stubs for the
  Delegate trait type. This has been fixed. (#1556)
• The Function and Method trait types will no longer fail when
  arguments are passed. Note that these trait types are already deprecated, and
  should not be used in new code. (#1543)
• Inner traits of a Union trait are now validated properly. Previously, in
  trait declarations like foo = Union(List(Int), Str), the list entries
  would not be validated. (#1522, #1534)
• Traits with a dynamic default that appear as inner traits of a Tuple
  trait are now validated properly. (#1521)
• A potential race condition in ListenerHandler has been fixed. The
  race condition is hard to exercise and has not been witnessed in the wild.
  (#1495)
• Use of add_class_trait to add a List trait was broken in the presence
  of subclasses. This has been fixed. (#1461)
• A use of the (deprecated) distutils library has been replaced with
  sysconfig. (#1452)
• Dynamic default handing has been fixed in the _instance_handler_factory
  used by the TraitsUI TableEditor. (#1446, #1450)
• The trait descriptions (the "info" text) for the File and Directory
  traits have been fixed to avoid giving a misleading error message when
  exists=True. (#1440)
• Clones of BaseInstance traits didn't correctly respect the allow_none
  parameter. This is now fixed. (#1433)
• An outdated reference to the "pyglet" Kiva backend has been removed. (#1431)

Documentation

• Brief installation docs have been added. (#1559)
• Occurrences of Any(some_list) in docs have been replaced. (#1547)
• The documentation for sync_trait has been updated to note that it only
  synchronises items for List traits, not for Dict and Set traits.
  (#1519)
• A configuration file for Read the Docs has been added. (#1478)
• A DeprecationWarning arising from an unnecessary override of the
  add_content method in the TraitDocumenter has been fixed. (#1475)
• The Sphinx version was temporarily pinned to avoid build failures arising
  from bugs in Sphinx 4.0.1. That pin has since been reverted.
  (#1471, #1462)
• Various docstring fixes have been applied. (#1468, #1465)
• Various typo fixes have been applied. (#1458, #1442)
• References to HasTraits.set have been rep...

Traits 6.2.0

Traits 6.2 is the latest feature release in the Traits 6 series, with several
improvements and fixes over Traits 6.1.

Highlights of this release

• The Traits examples are now distributed as part of the Traits egg, and
  are contributed to the etsdemo application. (The latter can be
  installed from PyPI with pip install etsdemo.)
• Performance of the observe framework has been significantly improved.
• It's no longer necessary to specify a trait comparison mode of
  ComparisonMode.identity when using observe to observe items
  in a List, Dict or Set.
• Support for Python 3.5 has been dropped.
• When importing from Traits, you should always import from one of the api
  modules (for example, traits.api, traits.adaptation.api, etc.) This
  recommendation has now been made explicit in the documentation. If you find
  something you need that's not available from one of the api modules,
  please let the Traits developers know.

Detailed PR-by-PR changes

More than 60 PRs went into this release. The following people contributed to
this release:

• Aaron Ayres
• Alexandre Chabot-Leclerc
• Kit Choi
• Mark Dickinson
• Kevin Duff
• Glen Granzow
• Matt Hancock
• Rahul Poruri
• Eric Prestat
• Kuya Takami
• Hugo van Kemenade
• Aditya Vats
• Corran Webster

Features

• The Property trait type now supports the observe keyword. (#1175,
  #1400)
• Add |= support to TraitDict for Python 3.9 and later. (#1306)
• Add casting keyword to numeric array types. (#547)
• The Traits examples are now part of the Traits package, and so are
  contributed to etsdemo. (#1275)
• The Traits examples package now includes a beginner's tutorial. (#1061)

Performance

• Parsing of the observe string was previously a performance bottleneck.
  This has been fixed, by removing some redundant parsing calls and by caching
  parsing results. (#1343, #1344, #1345)

Changes

• The NoDefaultSpecified constant (used as a default value for
  the TraitType default_value argument) is now public, made
  available from traits.api. (#1384, #1380, #1378)
• The deprecation of the TraitMap trait type has been reversed, because
  there are existing uses of TraitMap that are hard to replace.
  Nevertheless, it is still not recommended to use TraitMap in new code.
  Use Map instead. (#1365)
• An attempt to use PrefixList with an empty list, or PrefixMap or
  Map with an empty dictionary, now raises ValueError. As a result,
  the default default value (which used to be None) is always valid.
  (#1351)
• TraitListEvent arguments are now keyword only. (#1346)
• It's no longer necessary to specify a trait comparison mode of
  ComparisonMode.identity when using observe to observe items
  in a List, Dict or Set. (#1165, #1328, #1240)

Deprecations

• The Function and Method trait types are deprecated. Use
  Callable or Instance instead. (#1399, #1397)
• The edit parameter to configure_traits has been deprecated. (#1311)
• The UnittestTools._catch_warnings function has been deprecated. (#1310)
• The use of the CHECK_INTERFACES global variable for automated
  interface checking has been deprecated. (#1231)

Fixes

• Non-TraitError exceptions raised during Tuple validation are now
  propagated. Previously they were converted into TraitError. (#1393)
• Dynamic Range and Enum traits are now properly validated
  when inside a container (for example Tuple or List). Previously
  no validation was performed. (#1388, #1392)
• Remove the unused module-level constant traits.has_traits.EmptyList.
  (#1366)
• Don't hard-code class names in __repr__ implementations of
  TraitListEvent, TraitSetEvent and TraitDictEvent. (#1335)
• Don't notify on empty update\ s of Dict traits. (#1308)
• Fix exception raised when assigning a NumPy array to a List
  trait. (#1278)
• Fix uses of deprecated logger.warn function. (#1283)
• Fix a bad Instance trait declaration for a private trait in
  the _TraitChangeCollector class. (#1411)

Documentation

• Add "Tutorial" section to the main documentation, based on the
  new traits.examples tutorial content. (#1374)
• Clarify that only the api modules should be used for imports. (#1387)
• Update copyright header end years. (#1376)
• Update contents of image_LICENSE.txt. (#1362)
• Remove mentions of the removed functions adapts and implements from
  the examples and tutorial. (#1367)
• Move Traits introduction description to index.rst. (#1358)
• Fix path to Enthought logo when building docset. (#1285)
• Fix the trait_documenter extension to be less fragile. (#1247)
• Add user manual documentation for the Instance trait type. (#1395)
• Document that the List, Dict and Set trait types copy on
  assignment. (#1402)
• Various other minor improvements, typo fixes, and other documentation fixes.
  (#1396, #1383, #1381, #1384, #1292, #1355, #1350, #1319, #1292, #1401)

Cleanup and other maintenance

• Remove dead code. (#1281)
• Update super usage to the usual Python 3 argument-less pattern. (#1280)
• Remove per-import # noqa comments in api modules in favour of
  per-file ignores in the flake8 configuration. (#1269)
• Remove out-of-date and non-functional coverage badge from README. (#1263)
• Rename _i_observable module to i_observable. (#1296)
• Refactor and simplify method checks. (#1176)
• Fix typo in optional_dependencies comment. (#1235)
• Use ComparisonMode constants instead of magic numbers. (#1229)

Test suite

• Prevent test_enum failures if traitsui or GUI toolkit are not installed.
  (#1349)
• Tests that require pkg_resources are skipped if setuptools is not
  installed. (#1301)
• Fix an order-dependency bug in the test_subclasses_weakref regression
  test. (#1290)
• Fix a typo in a test method name. (#1309)
• Various additional or improved tests for existing code.
  (#1359, #1336, #1330, #1248, #1225, #1208, #1209)

Build and development workflow changes

• Traits now uses GitHub Actions for continuous integration. The Travis CI
  and Appveyor configurations have been removed. (#1296, #1360)
• CI runs are no longer based on EDM. (#878)
• New CI run for the core test suite, without any optional dependencies.
  (#1314)
• Test Python 3.9 in the continuous integration (and drop tests for Python
  3.5 and older). (#1326, #1313, , #1303)
• Make traits.examples into a package. (#1348)
• Make examples directories flake8-clean. (#1353)
• Fix examples packaging nit. (#1363)
• Support -h for getting help in etstool.py. (#1347)
• Add shell command to etstool.py. (#1293)
• Use the flake8_ets package in place of the local copyright_header
  package.
  The copyright_header package has been removed. (#1341)
• Add script check_observe_timing.py to benchmark performance of
  observe to compare with on_trait_change. (#1331)
• Correct the minimum Sphinx version in README. (#1216, #1320)
• Restrict Sphinx version to avoid buggy versions. (#1276)
• Make mypy an optional dependency. (#1289)
• Speed up CI builds for Travis and Appveyor by caching the pip directory
  (now redundant). (#1241)
• Add automated wheel and sdist building for Traits releases. (#1404, #1291)
• Add cron-job workflow to regularly test install of the latest releases
  from PyPI. (#1406)

Traits 6.1.1

Traits 6.1.1 is a bugfix release fixing a handful of minor documentation and
test-related issues with the Traits 6.1.0 release. There are no API-breaking
changes in this release. It's recommended that all users of Traits 6.1.0
upgrade to Traits 6.1.1.

Fixes

• Don't mutate global state at import time in a test module. (#1222)
• Standardize and fix copyright years in source files. (#1227, #1198)
• Fix trait-documenter extension tests for Sphinx 3.1. (#1206)
• Fix trait-documenter extension to handle properties correctly. (#1246)

Documentation fixes

• Expand user manual to mention dispatch. (#1195)
• Fix some spelling and grammar errors in the user manual. (#1210)
• Fix description in README to match the one in the setup script. (#1219)
• Update PyPI links and capitalization in README.rst. (#1250)
• Fix user manual mentioning a nonexisting feature in metadata filter. (#1207)
• Fix typo in comment in optional_dependencies. (#1235)

Traits 6.1.0

Released: 2020-06-05

The Traits library is a foundational component of the Enthought Tool Suite. It
provides observable, typed attributes for Python classes, making those classes
suitable for event-driven dataflow programming and for immediate use as models
for graphical user interfaces, like those provided by the TraitsUI library.

Traits 6.1 is the latest feature release in the Traits 6 series, and contains
several major improvements.

Highlights of this release

• A new observation framework for observing traited
  attributes and other observable objects has been introduced. This is intended
  to provide a full replacement for the existing on_trait_change
  mechanism, and aims to fix a number of fundamental flaws and limitations of
  that mechanism. See the observe-notification section of
  the user manual for an introduction to this framework.

• New TraitList, TraitDict and TraitSet classes have been added,
  subclassing Python's built-in list, dict and
  set (respectively). Instances of these classes are observable
  objects in their own right, and it's possible to attach observers to them
  directly. These classes were primarily introduced to support the new
  observation framework, and are not expected to be used directly. The API for
  these objects and their notification system is provisional, and may change in
  a future Traits release.

• A new Union trait type has been added. This is intended as a
  simpler replacement for the existing Either trait type, which
  will eventually be deprecated.

• New PrefixList, PrefixMap and Map trait types
  have been added. These replace the existing TraitPrefixList,
  TraitPrefixMap and TraitMap subclasses of
  TraitHandler, which are deprecated.

• Typing stubs for the Traits library have been added in a
  traits-stubs package, which will be released separately to PyPI. This
  should help support Traits-using projects that want to make use of type
  annotations and type checkers like mypy.

Notes on upgrading

As far as possible, Traits 6.1 is backwards compatible with Traits 6.0.
However, there are a few things to be aware of when upgrading.

• Traits 6.1 is not compatible with TraitsUI versions older than TraitsUI 7.0.
  A combination of Traits 6.1 or later with TraitsUI 6.x or earlier will fail
  to properly recognise View class variables as
  TraitsUI views, and an error will be raised if you attempt to create a
  TraitsUI view.

• Traits now does no logging configuration at all, leaving all such
  configuration to the application.

  In more detail: trait notification handlers should not raise exceptions in
  normal use, so an exception is logged whenever a trait notification handler
  raises. This part of the behaviour has not changed. What has changed is the
  way that logged exception is handled under default exception handling.

  Previously, Traits added a logging.StreamHandler to the
  top-level "traits" logger, so that trait notification exceptions would
  always be visible. Traits also added a logging.NullHandler to that
  logger. Both of those handlers have now been removed. We now rely on
  Python's "handler of last resort", which will continue to make notification
  exceptions to the user visible in the absence of any application-level
  log configuration.

• When listening for changes to the items of a List trait, an index
  or slice set operation no longer performs an equality check between the
  replaced elements and the replacement elements when deciding whether to issue
  a notification; instead, a notification is always issued if at least one
  element was replaced. For example, consider the following class:

  class Selection(HasTraits):
      indices = List(Int)
  
      @on_trait_change("indices_items")
      def report_change(self, event):
          print("Indices changed: ", event)
  

  When replacing the 8 with the same integer, we get this behavior:

  >>> selection = Selection(indices=[2, 5, 8])
  >>> selection.indices[2] = 8
  Indices changed:  TraitListEvent(index=2, removed=[8], added=[8])
  

  Previously, no notification would have been issued.

• The Color, RGBColor and Font trait factories
  have moved to TraitsUI, and should be imported from there rather than from
  Traits. For backwards compatibility, the factories are still
  available in Traits, but they are deprecated and will eventually
  be removed.

• As a reminder, the Unicode and Long trait types are
  deprecated since Traits 6.0. Please replace uses with Str and
  Int respectively. To avoid excessive noise in Traits-using
  projects, Traits does not yet issue deprecation warnings for existing uses of
  Unicode and Long. Those warnings will be introduced in a
  future Traits release, prior to the removal of these trait types.

Pending deprecations

In addition to the deprecations listed in the changelog below, some parts of
the Traits library are not yet formally deprecated, but are likely to be
deprecated before Traits 7.0. Users should be aware of the following possible
future changes:

• The Either trait type will eventually be deprecated. Where
  possible, use Union instead. When replacing uses of
  Either with Union, note that there are some significant
  API and behavioral differences between the two trait types, particularly with
  respect to handling of defaults. See the user manual for
  more details.

• The trait_modified event trait that's present on all HasTraits
  subclasses will eventually be removed. Users should not rely on it being
  present in an object's class_traits dictionary.

• Trait names starting with trait, traits, _trait or
  _traits may become reserved for use by ETS at some point in the future.
  Avoid using these names for your own traits.

Detailed PR-by-PR changes

More than 160 PRs went into this release. The following people contributed
code changes for this release:

• Ieva Cernyte
• Kit Yan Choi
• Maxime Costalonga
• Mark Dickinson
• Matt Hancock
• Midhun Madhusoodanan
• Shoeb Mohammed
• Franklin Ventura
• Corran Webster

Features

• Add os.PathLike support for Directory traits. (#867)
• Add Union trait type. (#779, #1103, #1107, #1116, #1115)
• Add PrefixList trait type. (#871, #1142, #1144, #1147)
• Add allow_none flag for Callable trait. (#885)
• Add support for type annotation. (#904, #1064)
• Allow mutable values in Constant trait. (#929)
• Add Map and PrefixMap trait types. (#886, #953, #956, #970, #1139,
  #1189)
• Add TraitList as the base list object that can perform validation
  and emit change notifications. (#912, #981, #984, #989, #999, #1003, #1011,
  #1026, #1009, #1040, #1172, #1173)
• Add TraitDict as the base dict object that can perform validation and
  emit change notifications. (#913)
• Add TraitSet as the base set object that can perform validation and
  emit change notifications. (#922, #1043)
• Implement observe to supersede on_trait_change for observing trait
  changes. (#976, #1000, #1007, #1065, #1023, #1066, #1070, #1069, #1067,
  #1080, #1082, #1079, #1071, #1072, #1075, #1085, #1089, #1078, #1093, #1086,
  #1077, #1095, #1102, #1108, #1110, #1112, #1117, #1118, #1123, #1125, #1126,
  #1128, #1129, #1135, #1156)

Changes

• GUI applications using Traits 6.1 will require TraitsUI >= 7.0. (#1134)
• TraitSetEvent and TraitDictEvent initialization arguments are now
  keyword-only. (#1036)
• TraitListObject will no longer skip notifications even if mutations
  result in content that compares equally to the old values. (#1026)
• TraitListEvent.index reported by mutations to a list is now normalized.
  (#1009)
• The default notification error handler for Traits no longer configures
  logging, and the top-level NullHandler log handler has been removed.
  (#1161)

Fixes

• Allow assigning None to CTrait.post_setattr. (#833)
• Fix reference count error. (#907)
• Improve HasTraits introspection with dir(). (#927)
• Fix the datetime-to-str converters used in DatetimeEditor. (#937)
• Raise TraitNotificationError on trailing comma in on_trait_change.
  (#926)
• Fix exception swallowing by Trait attribute access. (#959, #960)
• Allow collections in valid values for Enum trait. (#889)
• Fix TraitError when mutating a list/dict/set inside another container.
  (#1018)
• Fix setting default values via dynamic default methods or overriding trait in
  subclasses for mapped traits, used by Map, Expression, PrefixMap.
  (#1091, #1188)
• Fix setting default values via dynamic default methods or overriding trait in
  subclasses for Expression and AdaptsTo. (#1088, #1119, #1152)

Deprecations

• traits.testing.nose_tools is deprecated. (#880)
• SingletonHasTraits, SingletonHasStrictTraits and
  SingletonHasPrivateTraits are deprecated. (#887)
• TraitMap is deprecated, use Map instead. (#974)
• TraitPrefixMap is deprecated, use PrefixMap instead. (#974)
• TraitPrefixList is deprecated, use PrefixList. (#974)
• Color, RBGColor and Font are now deprecated. Use the ones from
  TraitsUI instead. (#1022)

Removals

• traits_super is removed. (#1015)

Documentation

• Add details on creating custom trait properties. (#387)
• Cross reference special handler signatures for listening to nested attributes
  in list and dict. (#894)
• Replace 'Traits 5' with 'Traits 6' in the documentation. (#903)
• Use major.minor version in documentation. (#1124)
• Add initial documentation on Traits internals. (#958)
• Fix example class OddInt. (#973)
• Add Dos and Donts for writing change handle...