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attrs: Attributes Without Boilerplate

.. image:: https://readthedocs.org/projects/attrs/badge/?version=stable :target: http://attrs.readthedocs.io/en/stable/?badge=stable :alt: Documentation Status

.. image:: https://travis-ci.org/hynek/attrs.svg?branch=master :target: https://travis-ci.org/hynek/attrs :alt: CI status

.. image:: https://codecov.io/github/hynek/attrs/branch/master/graph/badge.svg :target: https://codecov.io/github/hynek/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 <http://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 C(object): ... x = attr.ib(default=42) ... y = attr.ib(default=attr.Factory(list)) ... ... def hardmath(self, z): ... return self.x * self.y * z i = C(x=1, y=2) i C(x=1, y=2) i.hardmath(3) 6 i == C(1, 2) True i != C(2, 1) True attr.asdict(i) {'y': 2, 'x': 1} C() C(x=42, y=[]) C2 = attr.make_class("C2", ["a", "b"]) C2("foo", "bar") C2(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 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

Im 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 Ive see it used in.

-- Glyph Lefkowitz, inventor of Twisted and Software Developer at Rackspace in The One Python Library Everyone Needs <https://glyph.twistedmatrix.com/2016/08/attrs.html>_

I'm increasingly digging your attr.ocity. Good job!

-- ukasz Langa, prolific CPython core developer and Production Engineer at Facebook

.. -end-

.. -project-information-

Project Information

attrs is released under the MIT <http://choosealicense.com/licenses/mit/>_ license, its documentation lives at Read the Docs <https://attrs.readthedocs.io/>, the code on GitHub <https://github.com/hynek/attrs>, and the latest release on PyPI <https://pypi.org/project/attrs/>_. Its rigorously tested on Python 2.7, 3.4+, and PyPy.

Release Information

16.3.0 (2016-11-24)

Changes: ^^^^^^^^

Attributes now can have user-defined metadata which greatly improves attrs's extensibility. #96 <https://github.com/hynek/attrs/pull/96>_
Allow for a __attrs_post_init__ method that -- if defined -- will get called at the end of the attrs-generated __init__ method. #111 <https://github.com/hynek/attrs/pull/111>_
Add @attr.s(str=True) that will optionally create a __str__ method that is identical to __repr__. This is mainly useful with Exception\ s and other classes that rely on a useful __str__ implementation but overwrite the default one through a poor own one. Default Python class behavior is to use __repr__ as __str__ anyways.

If you tried using attrs with Exception\ s and were puzzled by the tracebacks: this option is for you.
Don't overwrite __name__ with __qualname__ for attr.s(slots=True) classes. #99 <https://github.com/hynek/attrs/issues/99>_

Full changelog <https://attrs.readthedocs.io/en/stable/changelog.html>_.

Credits

attrs is written and maintained by Hynek Schlawack <https://hynek.me/>_.

The development is kindly supported by Variomedia AG <https://www.variomedia.de/>_.

A full list of contributors can be found in GitHub's overview <https://github.com/hynek/attrs/graphs/contributors>_.

Its the spiritual successor of characteristic <https://characteristic.readthedocs.io/>_ and aspires to fix some of it clunkiness and unfortunate decisions. Both were inspired by Twisteds FancyEqMixin <https://twistedmatrix.com/documents/current/api/twisted.python.util.FancyEqMixin.html>_ but both are implemented using class decorators because sub-classing is bad for you <https://www.youtube.com/watch?v=3MNVP9-hglc>_, mkay?