attrs 20.2.0

Classes Without Boilerplate

attrs: Classes Without Boilerplate

attrs is the Python package that will bring back the joy of writing classes by relieving you from the drudgery of implementing object protocols (aka dunder methods).

Its main goal is to help you to write concise and correct software without slowing down your code.

For that, it gives you a class decorator and a way to declaratively define the attributes on that class:

>>> import attr

>>> @attr.s
... class SomeClass(object):
...     a_number = attr.ib(default=42)
...     list_of_numbers = attr.ib(factory=list)
...
...     def hard_math(self, another_number):
...         return self.a_number + sum(self.list_of_numbers) * another_number


>>> sc = SomeClass(1, [1, 2, 3])
>>> sc
SomeClass(a_number=1, list_of_numbers=[1, 2, 3])

>>> sc.hard_math(3)
19
>>> sc == SomeClass(1, [1, 2, 3])
True
>>> sc != SomeClass(2, [3, 2, 1])
True

>>> attr.asdict(sc)
{'a_number': 1, 'list_of_numbers': [1, 2, 3]}

>>> SomeClass()
SomeClass(a_number=42, list_of_numbers=[])

>>> C = attr.make_class("C", ["a", "b"])
>>> C("foo", "bar")
C(a='foo', b='bar')

After declaring your attributes attrs gives you:

• a concise and explicit overview of the class’s attributes,

• a nice human-readable __repr__,

• a complete set of comparison methods (equality and ordering),

• an initializer,

• and much more,

without writing dull boilerplate code again and again and without runtime performance penalties.

On Python 3.6 and later, you can often even drop the calls to attr.ib() by using type annotations.

This gives you the power to use actual classes with actual types in your code instead of confusing tuples or confusingly behaving namedtuples. Which in turn encourages you to write small classes that do one thing well. Never again violate the single responsibility principle just because implementing __init__ et al is a painful drag.

Getting Help

Please use the python-attrs tag on StackOverflow to get help.

Answering questions of your fellow developers is also great way to help the project!

Project Information

attrs is released under the MIT license, its documentation lives at Read the Docs, the code on GitHub, and the latest release on PyPI. It’s rigorously tested on Python 2.7, 3.5+, and PyPy.

We collect information on third-party extensions in our wiki. Feel free to browse and add your own!

If you’d like to contribute to attrs you’re most welcome and we’ve written a little guide to get you started!

attrs for Enterprise

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Release Information

20.2.0 (2020-09-05)

Backward-incompatible Changes

• attr.define(), attr.frozen(), attr.mutable(), and attr.field() remain provisional.

  This release fixes a bunch of bugs and ergonomics but they remain mostly unchanged.

  If you wish to use them together with mypy, you can simply drop this plugin into your project.

  Feel free to provide feedback to them in the linked issue #668.

  We will release the attrs namespace once we have the feeling that the APIs have properly settled. #668

Changes

• attr.define() et al now correct detect __eq__ and __ne__. #671

• attr.define() et al’s hybrid behavior now also works correctly when arguments are passed. #675

• It’s possible to define custom __setattr__ methods on slotted classes again. #681

• In 20.1.0 we introduced the inherited attribute on the attr.Attribute class to differentiate attributes that have been inherited and those that have been defined directly on the class.

  It has shown to be problematic to involve that attribute when comparing instances of attr.Attribute though, because when sub-classing, attributes from base classes are suddenly not equal to themselves in a super class.

  Therefore the inherited attribute will now be ignored when hashing and comparing instances of attr.Attribute. #684

• zope.interface is now a “soft dependency” when running the test suite; if zope.interface is not installed when running the test suite, the interface-related tests will be automatically skipped. #685

• The ergonomics of creating frozen classes using @define(frozen=True) and sub-classing frozen classes has been improved: you don’t have to set on_setattr=None anymore. #687

Full changelog.

Credits

attrs is written and maintained by Hynek Schlawack.

The development is kindly supported by Variomedia AG.

A full list of contributors can be found in GitHub’s overview.

It’s the spiritual successor of characteristic and aspires to fix some of it clunkiness and unfortunate decisions. Both were inspired by Twisted’s FancyEqMixin but both are implemented using class decorators because subclassing is bad for you, m’kay?