Sourced from attrs's releases.

26.1.0

Highlights

The main outward change here only affects people using field transformers, but it should be a nice quality of life improvement!

Full changelog below!

Special Thanks

This release would not be possible without my generous sponsors! Thank you to all of you making sustainable maintenance possible! If you would like to join them, go to https://github.com/sponsors/hynek and check out the sweet perks!

Above and Beyond

Variomedia AG (@variomedia), Tidelift (@tidelift), Kraken Tech (@kraken-tech), Privacy Solutions GmbH (@privacy-solutions), FilePreviews (@filepreviews), Ecosystems (@ecosyste-ms), TestMu AI Open Source Office (Formerly LambdaTest) (@LambdaTest-Inc), Doist (@Doist), Daniel Fortunov (@asqui), and Kevin P. Fleming (@kpfleming).

Maintenance Sustainers

Buttondown (@buttondown), Christopher Dignam (@chdsbd), Magnus Watn (@magnuswatn), David Cramer (@dcramer), Rivo Laks (@rivol), Polar (@polarsource), Mike Fiedler (@miketheman), Duncan Hill (@cricalix), Colin Marquardt (@cmarqu), Pieter Swinkels (@swinkels), Nick Libertini (@libertininick), Brian M. Dennis (@crossjam), Celebrity News AG (@celebritynewsag), The Westervelt Company (@westerveltco), Sławomir Ehlert (@slafs), Mostafa Khalil (@khadrawy), Filip Mularczyk (@mukiblejlok), Thomas Klinger (@thmsklngr), Andreas Poehlmann (@ap--), August Trapper Bigelow (@atbigelow), Carlton Gibson (@carltongibson), and Roboflow (@roboflow).

Full Changelog

Backwards-incompatible Changes

• Field aliases are now resolved before calling field_transformer, so transformers receive fully populated Attribute objects with usable alias values instead of None. The new Attribute.alias_is_default flag indicates whether the alias was auto-generated (True) or explicitly set by the user (False). #1509

Changes

• Fix type annotations for attrs.validators.optional(), so it no longer rejects tuples with more than one validator. #1496
• The attrs.validators.disabled() contextmanager can now be nested. #1513
• Frozen classes can set on_setattr=attrs.setters.NO_OP in addition to None. #1515
• It's now possible to pass attrs instances in addition to attrs classes to attrs.fields(). #1529

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This release contains contributions from @​bysiber, @​DavidCEllis, @​finite-state-machine, @​hynek, @​veeceey, and @​vstinner.

Artifact Attestations

You can verify this release's artifact attestions using GitHub's CLI tool by downloading the sdist and wheel from PyPI and running:

$ gh attestation verify --owner python-attrs attrs-26.1.0.tar.gz

... (truncated)

Sourced from attrs's changelog.

26.1.0 - 2026-03-19

Backwards-incompatible Changes

• Field aliases are now resolved before calling field_transformer, so transformers receive fully populated Attribute objects with usable alias values instead of None. The new Attribute.alias_is_default flag indicates whether the alias was auto-generated (True) or explicitly set by the user (False). #1509

Changes

• Fix type annotations for attrs.validators.optional(), so it no longer rejects tuples with more than one validator. #1496
• The attrs.validators.disabled() contextmanager can now be nested. #1513
• Frozen classes can set on_setattr=attrs.setters.NO_OP in addition to None. #1515
• It's now possible to pass attrs instances in addition to attrs classes to attrs.fields(). #1529

• 7bfc49e Prepare 26.1.0
• 31e0286 Update test_validators.py for Python 3.15a7 (#1530)
• 48b8611 Add instance support to attrs.fields() (#1529)
• 3a68d49 dev: document missing git tags failure mode
• a572c3a Allow field(on_setattr=NO_OP) on frozen classes
• af9c510 Fix validators.disabled() to save/restore state on nesting (#1513)
• ab7f8b2 update dev
• ce89f5d Fix message passing in frozen errors
• eccd966 Fix optional validator to accept tuples of len > 1 (#1496)
• e92fe52 policies: tighten screws (#1528)
• Additional commits viewable in compare view