Release 6.4.0

Released: 2022-08-12

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


  • 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)


  • 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)


  • 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)


  • 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)


  • 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 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)

Release 6.3.2

Released: 2021-11-10

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


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

Release 6.3.1

Released: 2021-10-12

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


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

Release 6.3.0

Released: 2021-10-08

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!


  • 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)


  • 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)


  • 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)


  • 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)


  • 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)


  • 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)

Release 6.2.0

Released: 2021-01-21

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 6.2 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


  • 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)


  • 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)


  • 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)


  • 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)


  • 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 updates 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)


  • 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 (#1347)

  • Add shell command to (#1293)

  • Use the flake8_ets package in place of the local copyright_header package. The copyright_header package has been removed. (#1341)

  • Add script 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)

Release 6.1.1

Released: 2020-07-23

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.


  • 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)

Release 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 Trait 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 StreamHandler to the top-level "traits" logger, so that trait notification exceptions would always be visible. Traits also added a 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)
        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 Migration from Either to Union 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


  • 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)


  • 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)


  • 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)


  • 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)


  • traits_super is removed. (#1015)


  • 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 handlers. (#1017)

  • Clarify when default initializer is called and when handlers are registered. (#1019)

  • Fix documentation rendering issues and front matter. (#1039, #1053)

  • Clarify when dynamic default values are considered to have existed. (#1068)

  • Expand user manual on container traits and objects. (#1058)

  • Add intersphinx support to configuration. (#1136)

  • Add user manual section on the new observe notification system. (#1060, #1140, #1143)

  • Add user manual section on the Union trait type and how to migrate from Either (#779, #1153, #1162)

  • Other minor cleanups and fixes. (#949, #1141, #1178)

Test suite

  • Allow tests to be skipped if TraitsUI is not installed. (#1038)

  • Add extras_require entry for testing. (#879)

  • Add tests for parsing on_trait_change mini-language. (#921)

  • Fix a missing import to allow a test module to be run standalone. (#961)

  • Add a GUI test for Enum.create_editor. (#988)

  • Fix some module-level DeprecationWarning messages. (#1157)

Build and continuous integration

  • CI no longer runs on Python 3.5 (#1044)

  • Add configobj dependency and remove remaining 3.5 references in (#1051)

  • Codecov reports are no longer retrieved for pull requests. (#1109)

  • CI tests requiring a GUI are now run against PyQt5 rather than PyQt4. (#1127)

  • Add Slack notifications for CI. (#1074)

  • Fix and improve various package metadata fields. (#1185)

Maintenance and code organization

  • Refactor CHasTraits traits_inited method. (#842)

  • Add support for prerelease section in version. (#864)

  • Rename comparison mode integer constants in ctraits.c. (#862)

  • Follow best practices when opening files. (#872)

  • Initialize cTrait getattr, setattr handlers in tp_new. (#875)

  • Check trait_change_notify early in call_notifiers. (#917)

  • Refactor ctraits.c for calling trait and object notifiers. (#918)

  • BaseEnum and Enum fixes and cleanup. (#968)

  • Split ctraits property api to _set_property and _get_property. (#967)

  • Fix overcomplicated __deepcopy__ implementation. (#992)

  • Add __repr__ implementation for TraitListEvent, TraitDictEvent and TraitSetEvent. (#1006, #1148, #1149)

  • Remove caching of editor factories. (#1032)

  • Remove conditional traitsui imports. (#1033)

  • Remove code duplication in (#1034)

  • Fix correctness in Enum default traitsui editor. (#1012)

  • Use NULL for zero-argument PyObject_CallMethod format. (#1100)

  • Miscellaneous other minor fixes, refactorings and cleanups. (#874, #882, #915, #920, #923, #924, #935, #939, #944, #950, #964)

Release 6.0.0

Released: 2020-02-14

No changes since the 6.0.0rc0 release candidate.

Release 6.0.0rc0

Released: 2020-01-30

Release notes

Traits 6.0 is a major update to the Traits package, with a number of backward incompatible changes from its predecessor. Notable changes:

  • Python 2.7 is no longer supported; Traits 6.0 requires Python 3.5 or later.

  • Trait types related to Python 2 (for example Unicode and Long) have been deprecated in favour of their Python 3 equivalents (for example Str and Int).

  • Many little-used historical features of Traits have been deprecated, and are scheduled for removal in Traits 7.0.

  • Some historical features of Traits that had no evidence of external usage were removed in Traits 6.0.

  • Introspection of CTrait and HasTraits objects is greatly improved. All of the internal state that was previously hidden within the C extension is now accessible from Python.

  • The Traits codebase has undergone some significant reorganizations, reformattings and style cleanups to make it easier to work with, and to improve the separation between Traits and TraitsUI.

  • This release was focused mainly on cleanup and bugfixing. Nevertheless, it contains a sprinkling of new features. There’s a new Datetime trait type. The Enum trait type now supports Python enumerations. The File trait type supports path-like objects.

More than 150 PRs went into this release. The following people contributed code changes for this release:

  • Kit Yan Choi

  • Mark Dickinson

  • Kevin Duff

  • Robert Kern

  • Midhun Madhusoodanan

  • Shoeb Mohammed

  • Sai Rahul Poruri

  • Corran Webster

  • John Wiggins

Porting guide

For the most part, existing code that works with Traits 5.2.0 should continue to work with Traits 6.0.0 without changes. However, there are some potentially breaking changes in Traits 6.0.0, and we recommend applying caution when upgrading.

Here’s a guide to dealing with some of the potentially breaking changes.

  • The Unicode and CUnicode trait types are now simply synonyms for Str and CStr. Unicode and CUnicode are considered deprecated. For now, no deprecation warning is issued on use of these deprecated trait types, but in Traits 6.1.0 and later, warnings may be issued, and in Traits 7.0.0 these trait types may be removed. It’s recommended that users update all uses of Unicode to Str and CUnicode to CStr to avoid warnings or errors in the future.

  • Similarly, Long and CLong are now synonyms for Int and CInt. The same recommendations apply as for the Unicode / Str trait types.

  • Uses of NO_COMPARE, OBJECT_IDENTITY_COMPARE and RICH_COMPARE should be replaced with the appropriate ComparisonMode enumeration members.

  • The validation for a Instance(ISomeInterface) trait type has changed, where ISomeInterface is a subclass of Interface. Previously, an assignment to such a trait validated the type of the assigned value against the interface, method by method. Now an isinstance check is performed against the interface instead. Make sure that classes implementing a given interface have the appropriate provides decorator.

    One notable side-effect of the above change is that plain mock.Mock instances can no longer be assigned to Instance(ISomeInterface) traits. To get around this, use spec=ISomeInterface when creating your mock object.

    This change does not affect Instance traits for non-interface classes.

  • The format of TraitListEvents has changed: for list events generated from a slice set or slice delete operation where that slice had a step other than 1, the added and removed fields of the event had an extra level of list wrapping (for example, added might be [[1, 2, 3]] instead of [1, 2, 3]). In Traits 6.0, this extra wrapping has been removed. There may be existing code that special-cased the extra wrapping.

  • Many classes and functions have moved around within the Traits codebase. If you have code that imports directly from Traits modules and subpackages instead of from traits.api or the other subpackage api modules, some of those imports may fail. To avoid potential for ImportError``s, you should import from ``traits.api whenever possible. If you find yourself needing some piece of Traits functionality that isn’t exposed in traits.api, and you think it should be, please open an issue on the Traits bug tracker.


  • Add new Datetime trait type. (#737, #814, #813, #815, #848)

  • Support Python Enums as value sets for the Enum trait. (#685, #828, #855)

  • Add Subclass alias for the Type trait type. (#739)

  • Add path-like support for the File trait. (#736)

  • Add new ComparisonMode enumeration type to replace the old NO_COMPARE, OBJECT_IDENTITY_COMPARE and RICH_COMPARE constants. The old constants are deprecated. (#830, #719, #680)

  • Add fast validation for Callable trait type; introduce new BaseCallable trait type for subclassing purposes. (#798, #795, #767)

  • Add CTrait.comparison_mode property to allow inspection and modification of a trait’s comparison mode. (#758, #735)

  • Add as_ctrait converter function to traits.api. This function converts a trait-like object or type to a CTrait, raising TypeError for objects that can’t be interpreted as a CTrait. It’s intended for use by users who want to create their own parameterised trait types.

    The as_ctrait feature comes with, and relies upon, a new informal interface: objects that can be converted to something of type CTrait can provide an zero-argument as_ctrait method that returns a new CTrait. Types can provide an instantiate_and_get_ctrait method, which when called with no arguments provides a new CTrait for that type. (#783, #794)

  • Add a new HasTraits._class_traits method for introspection of an object’s class traits. This parallels the existing HasTraits._instance_traits method. This method is intended for use in debugging. It’s not recommended for users to modify the returned dictionary. (#702)

  • Add CTrait.set_default_value method for setting information about the default of a CTrait. This provides an alternative to the previous method of using CTrait.default_value. The use of CTrait.default_value to set (rather than get) default information is deprecated. (#620)

  • Add new methods HasTraits._trait_notifications_enabled, HasTraits._trait_notifications_vetoed to allow introspection of the notifications states set by the existing methods HasTraits._trait_change_notify and HasTraits._trait_veto_notify. (#704)

  • Add TraitKind, ValidateTrait and DefaultValue Python enumeration types to replace previous uses of magic integers within the Traits codebase. (#680, #857)

  • The various CTrait internal flags are now exposed to Python as properties: CTrait.is_property (read-only), CTrait.modify_delegate, CTrait.setattr_original_value, CTrait.post_setattr_original_value, CTrait.is_mapped, and CTrait.comparison_mode. (#666, #693)


  • When pickling a CTrait, the py_post_setattr and py_validate fields are pickled directly. Previously, callables for those fields were replaced with a -1 sentinel on pickling. (#780)

  • A TraitListEvent is no longer emitted for a slice deletion which doesn’t change the contents of the list. (For example, del obj.mylist[2:] on a list that only has 2 elements.) (#740)

  • The added and removed attributes on a TraitListEvent are now always lists containing the added or removed elements. Previously, those lists were nested inside another list in some cases. (#771)

  • Change Instance(ISomeInterface) to use an isinstance check on trait set instead of using the dynamic interface checker. (#630)

  • Create an new AbstractViewElement abstract base class, and register the TraitsUI ViewElement as implementing it. This paves the way for removal of Traits UI imports from Traits. (#617)

  • ViewElements are now computed lazily, instead of at HasTraits subclass creation time. This removes a traitsui import from the trait.has_traits module. (#614)

  • The traits.util.clean_filename utility now uses a different algorithm, and should do a better job with accented and Unicode text. (#589)

  • Floating-point and integer checks are now more consistent between classes. In particular, BaseInt validation now matches Int validation, and Range type checks now match those used in Int and Float. (#588)

  • An exception other than TraitError raised during validation of a compound trait will now be propagated. Previously, that exception would be swallowed. (#581)

  • Traits no longer has a runtime dependency on the six package. (#638)

  • Use pickle protocol 3 instead of pickle protocol 1 when writing pickled object state to a file in configure_traits. (#796)

  • In traits.testing.optional_dependencies, make sure traitsui.api is available whenever traitsui is. (#616)

  • TraitInstance now inherits directly from TraitHandler instead of (the now removed) ThisClass. (#761)


  • Fix a use of the unsupported ValidateTrait.int_range. (#805)

  • Remove unnecessary copy method override from TraitSetObject. (#759)

  • Fix TraitListObject.clear to issue the appropriate items event. (#732)

  • Fix confusing error message when [None] passed into List(This(allow_none=False)). (#734)

  • Fix name-mangling of double-underscore private methods in classes whose name begins with an underscore. (#724)

  • Fix bytes_editor and password_editor bugs, and add tests for all editor factories. (#660)

  • Fix coercion fast validation type to do an exact type check instead of an instance check. This ensures that instances of subclasses of the target type are properly converted to the target type. For example, if True is assigned to a trait of type CInt, the resulting value is now 1. Previously, it was True. (#647)

  • Fix BaseRange to accept the same values as Range. (#583)

  • Fix integer Range to accept integer-like objects. (#582)

  • Fix floating-point Range to accept float-like values. (#579)

  • Fix a missing import in the adaptation benchmark script. (#575)

  • Fix issues with the filename argument to configure_traits. (#572)

  • Fix a possible segfault from careless field re-assignments in ctraits.c. (#844)


  • The NO_COMPARE, OBJECT_IDENTITY_COMPARE and RICH_COMPARE constants are deprecated. Use the corresponding members of the ComparisonMode enumeration instead. (#719)

  • The Unicode, CUnicode, BaseUnicode and BaseCUnicode trait types are deprecated. Use Str, CStr, BaseStr and BaseCStr instead. (#648)

  • The Long, CLong, BaseLong and BaseCLong trait types are deprecated. Use Int, CInt, BaseInt and BaseCInt instead. (#645, #573)

  • The AdaptedTo trait type is deprecated. Use Supports instead. (#760)

  • The following trait type aliases are deprecated. See the documentation for recommended replacments. false, true, undefined, ListInt, ListFloat, ListStr, ListUnicode, ListComplex, ListBool, ListFunction, ListMethod, ListThis, DictStrAny, DictStrStr, DictStrInt, DictStrFloat, DictStrBool, DictStrList. (#627)

  • Use of the filename argument to configure_traits (for storing state to or restoring state from pickle files) is deprecated. (#792)

  • The TraitTuple, TraitList and TraitDict trait handlers are deprecated. Use the Tuple, List and Dict trait types instead. (#770)

  • Use of CTrait.default_value for setting default value information is deprecated. Use CTrait.set_default_value instead. (#620)

  • Use of the rich_compare trait metadata is deprecated. Use the comparison_mode metadata instead. (#598)


  • Python 2 compatibility support code has been removed. (#638, #644)

  • Traits categories have been removed. (#568)

  • The following trait handlers have been removed: ThisClass, TraitClass, TraitExpression, TraitCallable, TraitString, TraitRange, TraitWeakRef. (#782, #711, #699, #698, #625, #593, #587, #640)

  • CTrait.rich_compare has been removed. (#598)

  • The cTrait.cast method has been removed. (#663)

  • The magical TraitValue and associated machinery have been removed. (#658)

  • The Generic trait type has been removed. (#657)

  • The UStr trait type and HasUniqueStrings class have been removed. (#654)

  • The str_find and str_rfind helper functions have been removed. (#633)

  • The global _trait_notification_handler has been removed. (#619)

  • BaseTraitHandler.repr has been removed. (#599)

  • HasTraits.trait_monitor was undocumented, untested, and broken, and has been removed. (#570)

  • The TraitInstance trait handler (not to be confused with the Instance trait type) no longer supports adaptation. (#641)

  • The DynamicView and HasDynamicViews classes have been removed from Traits and moved to TraitsUI instead. (#609)

  • DictStrLong has been removed. (#573)

Test suite

  • Fix various tests to be repeatable. (#802, #729)

  • Fix deprecation warnings in the test suite output. (#820, #804, #716)

  • Add machinery for testing unpickling of historical pickles. (#787)

  • Remove print statements from test suite. (#752, #768)

  • Fix a test to clean up the threads it creates. (#731)

  • Add tests for extended trait change issues #537 and #538 (#543)

  • Other minor test fixes. (#700, #821)


  • Improve documentation of trait container objects. (#810)

  • Improve documentation for the traits.ctraits module. (#826, #824, #659, #653, #829, #836)

  • Fix badly formatted TraitHandler documentation. (#817)

  • Fix and improve badly formatted trait types documentation. (#843)

  • Fix broken module links in section titles in API documentation. (#823)

  • Additional class docstring fixes. (#854)

  • Add changelog to built documentation, and absorb old changelog into the new one. (#800, #799)

  • Remove deprecated traits from the user manual. (#656)

  • Fix various Sphinx warnings (#717)

  • Use SVG badges in README (#567)

Build and continuous integration

  • Enable C asserts in Travis CI runs. (#791)

  • Abort CI on compiler warnings in Travis CI runs. (#769)

  • Run a flake8 check in both Travis CI and Appveyor runs. (#753, #762)

  • Checking copyright statements in Python files as part of CI runs. (#749)

  • Turn warnings into errors when building documentation in CI. (#744)

  • Add gnureadline as a development dependency on macOS and Linux. (#607)

  • Add an option to run tests quietly. (#606)

  • Enable the coverage extension for the documentation build. (#807)

  • Remove mocking in documentation configuration, and fix a deprecated configuration option. (#696)

Maintenance and code organization

This release includes a lot of refactoring and many minor improvements that will primarily benefit those working with the Traits codebase. These changes should not affect user-visible functionality. Here’s a summary of the more significant changes.

  • A major refactor has removed most of the circular dependencies between modules. (#730)

  • The codebase is now mostly flake8 clean. (#786, #753, #747, #748, #746, #595)

  • Copyright headers have been made consistent for all Python files. (#754)

  • ctraits.c has been run through clang-tidy and clang-format in order to bring it closer to PEP 7 style. (#715)

  • Editor factories have been moved into a new traits.editor_factories module, to help compartmentalize code dependencies on TraitsUI. (#661)

  • Trait container object classes (TraitDictObject, TraitListObject, TraitSetObject) have each been moved into their own module, along with their associated event type. (#677)

  • Miscellaneous other minor fixes, refactorings and cleanups. (#785, #777, #750, #726, #714, #712, #708, #701, #682, #665, #651, #652, #639, #636, #634, #626, #632, #611, #613, #612, #605, #603, #600, #597, #586, #585, #584, #580, #577, #578, #564, #806)

Release 5.2.0

Released: 2019-11-18


  • Support installation from source archives. (#528)


  • Ensure TraitListEvent.index is always an integer. (#548)

  • Update the deprecated collections.MutableMapping import. (#530)

  • Fix inadvertent modification of the Category base class. (#509)

  • Rework version handling in (#515)

  • Don’t autogenerate documentation for ViewElement. (#559)

  • Ensure that all tests are unittest compatible. (#551)


  • Replace occurences of deprecated AdaptsTo with Supports. (#532)

  • Remove Class trait. (#520)

  • Deprecate Category trait. (#510)

  • Fix typos in docstrings. (#502)

  • Use decorator form of classmethod. (#500)

  • Remove redefinition of NullHandler. (#518)

  • Add an import check helper. (#521)

  • Clean up Cython tests. (#555)

  • Clean up test output. (#553)


  • Update EDM version on CI to version 2.0.0. (#560)

  • Don’t finish fast on CI. (#556)

  • Use unittest to run tests in CI. (#552)

  • Low-level fixes and style cleanup in (#550)

  • Add --editable option for install, update CI commands. (#546)

  • Make git commit hash available to archives. (#526)

  • Fix use of non-edm envs as bootstrap envs on Windows. (#512)

  • Remove edm installed package before installing from source. (#516)

  • Add help text to click options. (#514)

  • Various cleanups, fixes and enhancements in (#511)

Release 5.1.2

Released: 2019-07-08


  • Traits documenter no longer generates bad reST for traits whose definition spans multiple source lines. (#494)

Release 5.1.1

Released: 2019-04-18


  • Revert a change (#449) which accidentally broke external uses of _py2to3.str_find and _py2to3.str_rfind. (#472)

Release 5.1.0

Released: 2019-04-15


  • Make UUID trait initializable. (#459)

  • Change default FileEditor behavior for a File trait based on whether exists=True is specified for that trait. (#451, #467)


  • The changes made in #373 to make dynamically-added traits pickleable have been reverted. (#462)

  • traits.api.python_version has been removed. Internals have been refactored to use six.PY2 in preference to sys.version_info. (#449)

  • Don’t depend on the 3rd party mock library on Python 3; use unittest.mock instead. (#446)


  • Fix a fragile NumPy-related test that failed (RuntimeError: empty_like method already has a docstring) with the newest version of NumPy. (#443)


  • traits._version.git_revision now gives the full commit hash (for local builds) instead of an abbreviated 7 hex-digit version. (#453)

  • Fix copyright years in documentation build. (#445)

  • Rename README.txt to README.rst, so that GitHub renders it nicely.

  • Code cleanups: remove “EOF” markers from code. Remove __main__ blocks for unit tests. Remove imports of unittest from unittest_tools. (#448, #446)

  • Update Travis CI and Appveyor configurations to run tests against all PR branches, not just PRs against master. (#466)

Release 5.0.0

Released : 30 January 2019

This major release accumulates more than an year’s worth of improvements, changes and bug fixes to the code base.

A few highlights of this release are :

  • Removal of 2to3 fixers and the use of six to provide Python 2/3 compatibility

  • Removal of deprecated traits.protocols submodule and related utils.

  • New HasRequiredTraits class

  • Better IPython tab completion for HasTraits subclasses

Changes summary since 4.6.0


  • CI for documentation (#431)

  • Remove 2to3 fixers (#430)

  • Enthought Sphinx Theme for docs (#427)

  • New HasRequiredTraits class (#419)

  • Free HasTraits subclasses from hashing/comparing by identity (#410)

  • Unify and fix default list editors (#396)

  • Add __dir__ method to HasTraits for IPython tab completion (#382)

  • Python 3 compatibility fixes (#374)

  • New context manager for setting trait-change-event tracer (#365)

  • Default trait type constants (#354)


  • Remove deprecated traits.protocols submodule and related utils (#435)

  • Fix invalid string escapes (#429)

  • Apply the “black” code reformatting utility on the Traits codebase (#432)

  • Update CI to use edm and etstool module (#420)

  • Clean up Float and BaseFloat validation (#393)

  • Merge master into Cython port (#370)

  • Docs and minor refactoring of MetaHasTraits class (#366)

  • Remove ridiculous premature optimization (#362)

  • Add support for PyInstaller app bundler (#361)

  • Add description and example for Either trait type (#360)

  • Drop support for Python 2.6 and Python < 3.4 (#345)

  • Add make target for docset to be used with Dash/Zeal (#180)


  • Fix odd error message and wrong exception type (#426)

  • Fix Color and RGBColor doc strings (#417)

  • Fix use of deprecared inspect.getargspec function (#408)

  • Fix extended names in on_trait_change lists (#404)

  • Support Unicode on trait documenter on Python 2.7 (#386)

  • Clear exception from Numpy properly (#377)

  • Fix pickling and deepcopying bug with dynamically added traits (#373)

  • Set auto_set/enter_set default once (#371)

  • Fix validation of This trait (#353)

  • Make cTrait.default_value_for raise a ValueError instead of seg faulting when asked for the default value of a trait that doesn’t have one. (#350)

  • Fix misuse of unittest.expectedFailure decorator (#346)

  • Fix issue with overridden HasTraits.trait function (#343)

Release 4.6.0

This is an incremental release over 4.5, accumulating over a year’s worth of bugfixes and small improvements to the code.

Highlights of this release include:

  • support for Python 3.4 and 3.5.

  • new Bytes and ValidatedTuple traits.

  • a new ArrayOrNone trait which correctly handles None comparisons with Numpy arrays.

  • clean-up of the ETSConfig code for TraitsUI toolkit selection.

  • better compatibility with NumPy scalar types.

  • many other bugfixes and improvements.

Change summary since 4.5.0


  • Added a Bytes Trait and related traits (#329)

  • Added support for finding resources from zipped Python source code (#316)

  • Added in-place set arithmetic operations for TraitSetObject``s and accept match behaviour of ``TraitSetObject with regular Python sets when performing operations with non-set types (eg. lists, dictionaries) (#289)

  • Added a context manager to allow provisional selection of a toolkit to ETSConfig (this generally improves reliability of toolkit selection for Pyface and TraitsUI). (#276)

  • Added Trait change recorder to aid in debugging event-driven code. (#139)

  • __iadd__ and __imul__ implemented on TraitListObjects. (#165)

  • Added new ArrayOrNone trait type to replace the Either(None, Array) idiom. The old idiom results in warnings on NumPy >= 1.9. (#219)

  • Added a new ValidatedTuple trait that supports custom validation. (#205)


  • Removed redundant, internal ETSConfig from Traits codebase. (#327)

  • Better error reporting for failed attribute access. (#243)

  • Removed buggy -toolkit commandline option ETSConfig. (#326)

  • Removed buggy *names positional arguments from on_trait_change decorator in improved argument passing (#207).

  • Allow Float and BaseFloat traits to accept Python longs. (#272)

  • Clean-up and fixes to example code. (#126)

  • Remove outdated ImportSpy and ImportManager utilities. (#188)

  • The deprecated decorator now issues a DeprecationWarning (using the Python warnings module) rather than logging a warning via the logging machinery. It no longer tries to remember when a warning has been previously issued. (#220)

  • Deprecated HasTraits.get() and HasTraits.set() (#190).

  • The default View shows all (non-event) traits whose visible property is not False. Private traits are set visible=False by default. (#234)


  • Fix Bool traits so that value stored is always a Python bool (and in particular, not a NumPy np.bool_). (#318)

  • Fix Bool traits so that regular validator accepts NumpPy’s np.bool_ boolean values (bringing it in agreement with the fast validator). (#302)

  • Fix use of next in TraitDocumenter for Python 3 compatibility. (#293)

  • Fix off-by-one error when TraitListObject is setting or deleting slices. (#283)

  • Fix reference cycles caused by sync_traits. (#135)

  • Fix so that sys.exc_info() works as expected in exception handlers in Python 3 (#266)

  • Fix String trait to accept str subclasses (like numpy.str_). (#267)

  • Fixed incorrect in list events for insert operations with an index outside the range [-len(target_list), len(target_list)]. (#165)

  • Fix incorrect behaviour of check_implements for overridden methods. (#192)

  • Fix error when trying to listen to traits using list bracket notation. (#195)

  • Fix reference leak in CHasTraits._notifiers. (#248)

  • Fix reference leak from use of DelegatesTo. (#260)

  • Instance traits weren’t included in the result of traits(). (#234)

Release 4.5.0

Traits is now compatible with Python 3! The library now supports Python 3.2 and 3.3.

The release also includes increased code coverage and automatic coverage report through

Change summary since 4.4.0


  • Test files cleanups (#108, #111, #121)

  • Add automatic coverage reports (#110, #122)

  • Removed obsolete code (#109, #112, #113)

  • Increased test coverage (#114, #118)

  • Python 3 support (#115). Thanks Yves Delley.

  • Allow setting and resetting the global adaptation manager (#145)

  • Various documentation improvements (#132, #133, #148, #154).


  • The Int trait type now accepts Python ints and Python longs, as well as instances of any Python type that implements the __index__ method. Previously, long instances were not accepted. (#104, #123).


  • Fix crash when trying to validate a property that has been deleted. (#138)

  • Fix clearing exception when raising a TraitError (#119)

  • Fix automatic adaptation when assigning to List trait (#147)

  • Fix some ctraits refcounting and exception clearing bugs (#48). Thanks Yves Delley.

Release 4.4.0

The major new feature in this release is a new adaptation mechanism in the traits.adaptation package. The new mechanism is intended to replace the older traits.protocols package. Code written against traits.protocols will continue to work, although the traits.protocols API has been deprecated, and a warning will be logged on first use of traits.protocols. See the ‘Advanced Topics’ section of the user manual for more details.

The release also includes improved support for using Cython with HasTraits classes, some new helper utilities for writing unit tests for Traits events, and a variety of bug fixes, stability enhancements, and internal code improvements.

Change summary since 4.3.0

New features

  • The adaptation mechanism in Traits, formerly based on the ‘traits.protocols’ package, has been replaced with the more robust ‘traits.adaptation’ package. (#51)

  • Added utility function for importing symbols (name, classes, functions) by name: ‘traits.util.api.import_symbol’. (#51)

  • Users can set a global tracer, which receives all traits change events: traits.trait_notifiers.set_change_event_tracers. (#79)


  • Update benchmark script. (#54)

  • traits.util.deprecated: use module logger instead of root logger. (#59)

  • Provide an informative message in AdaptationError. (#62)

  • Allow HasTraits classes to be cythonized. (#73)

  • Improve tests for cythonization support. (#75)

  • Extending various trait testing helpers (#53)


  • The Traits notification code has been reworked to remove code duplication, and test coverage of that code has been significantly improved. (#79)


  • Fix race condition when removing a traits listener. (#57)

  • Fix ugly interaction between DelegatesTo change handlers, dynamic change handlers and two levels of dynamic initialization. (#63)

  • Use a NullHandler for all ‘traits’ loggers. (#64)

  • Fix race condition in TraitChangeNotifyWrapper.listener_deleted (#66)

  • Fix leaking notifiers. (#68)

  • Fix failing special instance trait events. (#78)

  • Fix hiding KeyError exception inside trait default initialize method. (#81)

  • Fix Adapter object initialization. (#93)

  • Fix cyclic garbage arising from use of the WeakRef trait type. (#95)

  • TraitSetObject.copy now returns a plain rather than an uninitialized TraitSetObject instance. (#97)

  • Fix cyclic garbage arising from dynamic trait change handlers. (#101)

Releases 4.3.0 - 3.6.0

Changelogs unavailable.

Release 3.5.0

Released: 2010-10-15


  • adding support for drop-down menu in Button traits, but only for qt backend

  • adding ‘show_notebook_menu’ option to ListEditor so that the user can right-click and show or hide the context menu (Qt)

  • added selection range traits to make it possible for users to replace selected text


  • fixed null color editor to work with tuples

  • bug when opening a view with the ToolbarButton

Release 3.4.0

Released: 2010-05-26


  • adding new example to make testing rgb color editor easier


  • fixed NumericColumn to not expect object to have model_selection attribute, and removed more dead theming code

  • fixed API bugs with the NumericColumn where its function signatures differed from its base class, but the calling code expected them to all be the same

  • fixed bug which was related to type name errors caused when running Sphinx

  • when using File(exists=True), be sure to validate the type of the value first before using os.path.isfile()

Release 3.3.0

Released: 2010-02-24


The major enhancement this release is that the entire Traits package has been changed to use relative imports so that it can be installed as a sub-package inside another larger library or package. This was not previously possible, since the various modules inside Traits would import each other directly through “traits.[module]”. Many thanks to Darren Dale for the patch.


There have been numerous minor bugfixes since the last release. The most notable ones are:

  • Many fixes involve making Traits UI more robust if wxPython is not installed on a system. In the past, we have been able to use Qt if it was also installed, but removing Wx would lead to a variety of little bugs in various places. We’ve squashed a number of these. We’ve also added better checks to make sure we’re selecting the right toolkit at import and at runtime.

  • A nasty cyclic reference was discovered and eliminated in DelegatesTo traits.

  • The Undefined and Uninitialized Traits were made into true singletons.

  • Much of the inconsistent formatting across the entire Traits source has been eliminated and normalized (tabs/spaces, line endings).

Release 3.2.0

Released: 2009-07-15


  • Implemented editable_labels attribute in the TabularEditor for enabling editing of the labels (i.e. the first column)

  • Saving/restoring window positions works with multiple displays of different sizes

  • New ProgressEditor

  • Changed default colors for TableEditor

  • Added support for HTMLEditor for QT backend using QtWebKit

  • Improved support for opening links in external browser from HTMLEditor

  • Added support for TabularEditor for QT backend

  • Added support for marking up the CodeEditor, including adding squiggles and dimming lines

  • Added SearchEditor

  • Improved unicode support

  • Changed behavior of RangeEditor text box to not auto-set

  • Added support in RangeEditor for specifying the method to evaluate new values.

  • Add DefaultOverride editor factory courtesy Stéfan van der Walt

  • Removed sys.exit() call from SaveHandler.exit()