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 replaced with
  HasTraits.trait_set. (#1451)
• Some issues with the tutorial CSS used in the ETS demo application have been
  fixed; the colour scheme has been changed to Enthought colours. (#1421,
  #1419)

Cleanup and refactoring

• All built-in TraitType subclasses now provide the default value type directly
  rather than inferring it. (#1555, #1536, #1531, #1539, #1532, #1540)
• The trait_added and trait_modified traits on HasTraits now
  have proper trait type declarations. (#1552)
• Redundant unittest.main blocks have been removed. (#1545)
• Style fixes have been applied to trait_types.pyi. (#1523)
• ObserverExpression and other key observation classes now have more
  debug-friendly repr implementations. (#1514)
• The observer parsing internals have been reworked to make
  ObserverGraph the key "compiled" object that the rest of Traits cares
  about, rather than ObserverExpression. (#1512)
• The grammar and parser for the observe mini-language have been simplified.
  (#1506)
• Confusion between "any_trait" and "anytrait" in non-user-facing
  functions and classes has been cleaned up. (#1497)
• Unnecessary noqa markers have been removed. (#1499)
• A use of the property callable has been replaced with a property
  decorator. (#1470)
• A bad observe-decorated listener signature in a test has been fixed. (#1530)

Build and development workflow

• Python 3.10 is supported and tested, and wheels are built for Python 3.10.
  (#1425, #1567, #1569, #1571)
• Wheels are now built for Linux/aarch64. (#1567)
• Universal wheels are now built for macOS, to support Apple Silicon. (#1567)
• Cron jobs now send failure/success Slack notifications to Enthought's
  internal channel. (#1481)
• All cron jobs now include a workflow_dispatch trigger. (#1480)
• The main development branch is now called "main" rather than "master".
  (#1467)
• Automated tests have been added for PyPI wheels. (#1417)