By default, two instances of attrs classes are equal if all their fields are equal.
For that, attrs writes
__ne__ methods for you.
Additionally, if you pass
order=True, attrs will also create a full set of ordering methods that are based on the defined fields:
As with other features, you can exclude fields from being involved in comparison operations:
>>> from attrs import define, field >>> @define ... class C: ... x: int ... y: int = field(eq=False) >>> C(1, 2) == C(1, 3) True
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
>>> @define ... class S: ... x: str = field(eq=str.lower) >>> S("foo") == S("FOO") True >>> @define(order=True) ... class C: ... x: str = field(order=int) >>> C("10") > C("2") True
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
attrs.cmp_using() helper to create such functions.
For NumPy arrays it would look like this:
import numpy @define 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
define() (but not in
You can set both at once by using the cmp argument that we’ve undeprecated just for this use-case.