By default, two instances of attrs classes are equal if all their fields are equal. For that, attrs writes __eq__ and __ne__ methods for you.

Additionally, if you pass order=True (which is the default if you use the attr.s decorator), attrs will also create a full set of ordering methods that are based on the defined fields: __le__, __lt__, __ge__, and __gt__.


As with other features, you can exclude fields from being involved in comparison operations:

>>> from attr import define, field

>>> @define
... class C:
...     x: int
...     y: int = field(eq=False)

>>> C(1, 2) == C(1, 3)

Additionally you can also pass a callable instead of a bool to both eq and order. It is then used as a key function like you may know from sorted:

>>> from attr import define, field

>>> @define
... class S:
...     x: str = field(eq=str.lower)

>>> S("foo") == S("FOO")

>>> @define(order=True)
... class C:
...     x: str = field(order=int)

>>> C("10") > C("2")

This is especially useful when you have fields with objects that have atypical comparison properties. Common examples of such objects are NumPy arrays.

To save you unnecessary boilerplate, attrs comes with the attr.cmp_using helper to create such functions. For NumPy arrays it would look like this:

import numpy

class C:
   an_array = field(eq=attr.cmp_using(eq=numpy.array_equal))


Please note that eq and order are set independently, because order is False by default in attrs.define (but not in attr.s). You can set both at once by using the cmp argument that we’ve undeprecated just for this use-case.