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).
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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:
>>> from attrs import asdict, define, make_class, Factory
>>> @define
... class SomeClass:
... a_number: int = 42
... list_of_numbers: list[int] = 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
>>> asdict(sc)
{'a_number': 1, 'list_of_numbers': [1, 2, 3]}
>>> SomeClass()
SomeClass(a_number=42, list_of_numbers=[])
>>> C = 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__
, - equality-checking methods,
- an initializer,
- and much more,
without writing dull boilerplate code again and again and without runtime performance penalties.
Hate type annotations!?
No problem!
Types are entirely optional with attrs
.
Simply assign attrs.field()
to the attributes instead of annotating them with types.
This example uses attrs
's modern APIs that have been introduced in version 20.1.0, and the attrs
package import name that has been added in version 21.3.0.
The classic APIs (@attr.s
, attr.ib
, plus their serious-business aliases) and the attr
package import name will remain indefinitely.
Please check out On The Core API Names for a more in-depth explanation.
Data Classes
On the tin, attrs
might remind you of dataclasses
(and indeed, dataclasses
are a descendant of attrs
).
In practice it does a lot more and is more flexible.
For instance it allows you to define special handling of NumPy arrays for equality checks, or allows more ways to plug into the initialization process.
For more details, please refer to our comparison page.
Project Information
- License: MIT
- PyPI: https://pypi.org/project/attrs/
- Source Code: https://github.com/python-attrs/attrs
- Documentation: https://www.attrs.org/
- Changelog: https://www.attrs.org/en/stable/changelog.html
- Get Help: please use the
python-attrs
tag on StackOverflow - Contributing: https://github.com/python-attrs/attrs/blob/main/.github/CONTRIBUTING.md
- Third-party Extensions: https://github.com/python-attrs/attrs/wiki/Extensions-to-attrs
- Supported Python Versions: 3.6 and later (last 2.7-compatible release is 21.4.0)
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