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*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:
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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:
```pycon
>>> 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.
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