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attrs v21.1.0 Release Notes

Release Date: 2021-05-06 // almost 3 years ago

  • 🗄 Deprecations ^

    • The long-awaited, much-talked-about, little-delivered import attrs is finally upon us!

    Since the NG APIs have now been proclaimed stable, the next release of attrs will allow you to actually import attrs. We're taking this opportunity to replace some defaults in our APIs that made sense in 2015, but don't in 2021.

    So please, if you have any pet peeves about defaults in attrs's APIs, now is the time to air your grievances in #487! We're not gonna get such a chance for a second time, without breaking our backward-compatibility guarantees, or long deprecation cycles. Therefore, speak now or forever hold you peace! #487 <https://github.com/python-attrs/attrs/issues/487>_

    • The cmp argument to attr.s() and attr.ib() has been undeprecated It will continue to be supported as syntactic sugar to set eq and order in one go.

    I'm terribly sorry for the hassle around this argument! The reason we're bringing it back is it's usefulness regarding customization of equality/ordering.

    The cmp attribute and argument on attr.Attribute remains deprecated and will be removed later this year. #773 <https://github.com/python-attrs/attrs/issues/773>_

    🔄 Changes ^

    • It's now possible to customize the behavior of eq and order by passing in a callable. #435 <https://github.com/python-attrs/attrs/issues/435>, #627 <https://github.com/python-attrs/attrs/issues/627>
    • The instant favorite next-generation APIs <https://www.attrs.org/en/stable/api.html#next-gen>_ are not provisional anymore!

    They are also officially supported by Mypy as of their 0.800 release <https://mypy-lang.blogspot.com/2021/01/mypy-0800-released.html>_.

    We hope the next release will already contain an (additional) importable package called attrs. #668 <https://github.com/python-attrs/attrs/issues/668>, #786 <https://github.com/python-attrs/attrs/issues/786>

    • If an attribute defines a converter, the type of its parameter is used as type annotation for its corresponding __init__ parameter.

    If an attr.converters.pipe is used, the first one's is used. #710 <https://github.com/python-attrs/attrs/issues/710>_

    • 🛠 Fixed the creation of an extra slot for an attr.ib when the parent class already has a slot with the same name. #718 <https://github.com/python-attrs/attrs/issues/718>_
    • __attrs__init__() will now be injected if init=False, or if auto_detect=True and a user-defined __init__() exists.

    This enables users to do "pre-init" work in their __init__() (such as super().__init__()).

    __init__() can then delegate constructor argument processing to self.__attrs_init__(*args, **kwargs). #731 <https://github.com/python-attrs/attrs/issues/731>_

    • bool(attr.NOTHING) is now False. #732 <https://github.com/python-attrs/attrs/issues/732>_
    • It's now possible to use super() inside of properties of slotted classes. #747 <https://github.com/python-attrs/attrs/issues/747>_
    • Allow for a __attrs_pre_init__() method that -- if defined -- will get called at the beginning of the attrs-generated __init__() method. #750 <https://github.com/python-attrs/attrs/issues/750>_
    • ➕ Added forgotten attr.Attribute.evolve() to type stubs. #752 <https://github.com/python-attrs/attrs/issues/752>_
    • attrs.evolve() now works recursively with nested attrs classes. #759 <https://github.com/python-attrs/attrs/issues/759>_
    • 👍 Python 3.10 is now officially supported. #763 <https://github.com/python-attrs/attrs/issues/763>_
    • attr.resolve_types() now takes an optional attrib argument to work inside a field_transformer. #774 <https://github.com/python-attrs/attrs/issues/774>_
    • ClassVar\ s are now also detected if they come from typing-extensions <https://pypi.org/project/typing-extensions/>. #782 <https://github.com/python-attrs/attrs/issues/782>
    • To make it easier to customize attribute comparison (#435), we have added the attr.cmp_with() helper.

    See the new docs on comparison <https://www.attrs.org/en/stable/comparison.html>_ for more details. #787 <https://github.com/python-attrs/attrs/issues/787>_

    • Added provisional support for static typing in pyright via the dataclass_transforms specification <https://github.com/microsoft/pyright/blob/master/specs/dataclass_transforms.md>_. Both the pyright specification and attrs implementation may change in future versions of both projects.

    Your constructive feedback is welcome in both attrs#795 <https://github.com/python-attrs/attrs/issues/795>_ and pyright#1782 <https://github.com/microsoft/pyright/discussions/1782>. #796 <https://github.com/python-attrs/attrs/issues/796>