Classes Without Boilerplate
Project description
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). Trusted by NASA for Mars missions since 2020!
Its main goal is to help you to write concise and correct software without slowing down your code.
Sponsors
attrs would not be possible without our amazing sponsors. Especially those generously supporting us at the The Organization tier and higher:
Please consider joining them to help make attrs’s maintenance more sustainable!
Example
attrs 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.
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.
Check out On The Core API Names for an in-depth explanation!
Hate Type Annotations!?
No problem!
Types are entirely optional with attrs.
Simply assign attrs.field()
to the attributes instead of annotating them with types:
from attrs import define, field
@define
class SomeClass:
a_number = field(default=42)
list_of_numbers = field(factory=list)
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, allows more ways to plug into the initialization process, has a replacement for __init_subclass__
, and allows for stepping through the generated methods using a debugger.
For more details, please refer to our comparison page, but generally speaking, we are more likely to commit crimes against nature to make things work that one would expect to work, but that are quite complicated in practice.
Project Information
- Changelog
- Documentation
- PyPI
- Source Code
- Contributing
- Third-party Extensions
- Get Help: use the
python-attrs
tag on Stack Overflow
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.
Release Information
Backwards-incompatible Changes
-
attrs.evolve()
doesn't accept the inst argument as a keyword argument anymore. Pass it as the first positional argument instead. #1264 -
attrs.validators.provides()
has been removed. The removed code is available as a gist for convenient copy and pasting. #1265 -
All packaging metadata except from
__version__
and__version_info__
has been removed from theattr
andattrs
modules (for example,attrs.__url__
).Please use
importlib.metadata
or importlib_metadata instead. #1268 -
Speed up the generated
__eq__
methods significantly by generating a chain of attribute comparisons instead of constructing and comparing tuples. This change arguably makes the behavior more correct, but changes it if an attribute compares equal by identity but not value, likefloat('nan')
. #1310
Deprecations
- The repr_ns argument to
attr.s
is now deprecated. It was a workaround for nested classes in Python 2 and is pointless in Python 3. #1263 - The hash argument to
@attr.s
,@attrs.define
, andmake_class()
is now deprecated in favor of unsafe_hash, as defined by PEP 681. #1323
Changes
-
Allow original slotted
functools.cached_property
classes to be cleaned by garbage collection. Allowsuper()
calls in slotted cached properties. #1221 -
Our type stubs now use modern type notation and are organized such that VS Code's quick-fix prefers the
attrs
namespace. #1234 -
Preserve
AttributeError
raised by properties of slotted classes withfunctools.cached_properties
. #1253 -
It is now possible to wrap a converter into an
attrs.Converter
and get the current instance and/or the current field definition passed into the converter callable.Note that this is not supported by any type checker, yet. #1267
-
attrs.make_class()
now populates the__annotations__
dict of the generated class, so thatattrs.resolve_types()
can resolve them. #1285 -
Added the
attrs.validators.or_()
validator. #1303 -
The combination of a
__attrs_pre_init__
that takes arguments, a kw-only field, and a default on that field does not crash anymore. #1319 -
attrs.validators.in_()
now transforms certain unhashable options to tuples to keep the field hashable.This allows fields that use this validator to be used with, for example,
attrs.filters.include()
. #1320 -
If a class has an inherited method called
__attrs_init_subclass__
, it is now called once the class is done assembling.This is a replacement for Python's
__init_subclass__
and useful for registering classes, and similar. #1321
Project details
Release history Release notifications | RSS feed
Download files
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.