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.. image:: http://www.attrs.org/en/latest/_static/attrs_logo.png
:alt: attrs Logo
======================================
``attrs``: Classes Without Boilerplate
======================================
.. image:: https://readthedocs.org/projects/attrs/badge/?version=stable
:target: http://www.attrs.org/en/stable/?badge=stable
:alt: Documentation Status
.. image:: https://travis-ci.org/python-attrs/attrs.svg?branch=master
:target: https://travis-ci.org/python-attrs/attrs
:alt: CI Status
.. image:: https://codecov.io/github/python-attrs/attrs/branch/master/graph/badge.svg
:target: https://codecov.io/github/python-attrs/attrs
:alt: Test Coverage
.. 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).
Its main goal is to help you to write **concise** and **correct** software without slowing down your code.
.. -spiel-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(default=attr.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,
- an initializer,
- and much more,
*without* writing dull boilerplate code again and again and *without* runtime performance penalties.
This gives you the power to use actual classes with actual types in your code instead of confusing ``tuple``\ s or `confusingly behaving <http://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.
.. -testimonials-
Testimonials
============
**Amber Hawkie Brown**, Twisted Release Manager and Computer Owl:
Writing a fully-functional class using attrs takes me less time than writing this testimonial.
**Glyph Lefkowitz**, creator of `Twisted <https://twistedmatrix.com/>`_, `Automat <https://pypi.python.org/pypi/Automat>`_, and other open source software, in `The One Python Library Everyone Needs <https://glyph.twistedmatrix.com/2016/08/attrs.html>`_:
I’m looking forward to is being able to program in Python-with-attrs everywhere.
It exerts a subtle, but positive, design influence in all the codebases I’ve see it used in.
**Kenneth Reitz**, author of `requests <http://www.python-requests.org/>`_, Python Overlord at Heroku, `on paper no less <https://twitter.com/hynek/status/866817877650751488>`_:
attrs—classes for humans. I like it.
**Łukasz Langa**, prolific CPython core developer and Production Engineer at Facebook:
I'm increasingly digging your attr.ocity. Good job!
.. -end-
.. -project-information-
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 great way to help the project!
Project Information
===================
``attrs`` is released under the `MIT <https://choosealicense.com/licenses/mit/>`_ license,
its documentation lives at `Read the Docs <http://www.attrs.org/>`_,
the code on `GitHub <https://github.com/python-attrs/attrs>`_,
and the latest release on `PyPI <https://pypi.org/project/attrs/>`_.
Its rigorously tested on Python 2.7, 3.4+, and PyPy.
If you'd like to contribute you're most welcome and we've written `a little guide <http://www.attrs.org/en/latest/contributing.html>`_ to get you started!