.. raw:: html

.. teaser-begin

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 <https://nedbatchelder.com/blog/200605/dunder.html> methods).
Trusted by NASA <https://docs.github.com/en/account-and-profile/setting-up-and-managing-your-github-profile/customizing-your-profile/personalizing-your-profile#list-of-qualifying-repositories-for-mars-2020-helicopter-contributor-badge> for Mars missions since 2020!

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

.. teaser-end

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

.. -code-begin-

.. code-block:: pycon

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 <https://www.attrs.org/en/latest/types.html>_.

This gives you the power to use actual classes with actual types in your code instead of confusing tuple\ s or confusingly behaving <https://www.attrs.org/en/stable/why.html#namedtuples> namedtuple\ s.
Which in turn encourages you to write small classes that do one thing well <https://www.destroyallsoftware.com/talks/boundaries>.
Never again violate the single responsibility principle <https://en.wikipedia.org/wiki/Single_responsibility_principle>_ just because implementing __init__ et al is a painful drag.

.. -getting-help-

Getting Help

Please use the python-attrs tag on StackOverflow <https://stackoverflow.com/questions/tagged/python-attrs>_ to get help.

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

.. -project-information-

Project Information

attrs is released under the MIT <https://choosealicense.com/licenses/mit/> license,
its documentation lives at Read the Docs <https://www.attrs.org/>,
the code on GitHub <https://github.com/python-attrs/attrs>,
and the latest release on PyPI <https://pypi.org/project/attrs/>.
It’s rigorously tested on Python 2.7, 3.5+, and PyPy.

We collect information on third-party extensions in our wiki <https://github.com/python-attrs/attrs/wiki/Extensions-to-attrs>_.
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 <https://www.attrs.org/en/latest/contributing.html>_ to get you started!

attrs for Enterprise

Available as part of the Tidelift Subscription.

The maintainers of attrs and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source packages you use to build your applications.
Save time, reduce risk, and improve code health, while paying the maintainers of the exact packages you use.
Learn more. <https://tidelift.com/subscription/pkg/pypi-attrs?utm_source=pypi-attrs&utm_medium=referral&utm_campaign=enterprise&utm_term=repo>_