67 lines
1.9 KiB
ReStructuredText
67 lines
1.9 KiB
ReStructuredText
Comparison
|
|
==========
|
|
|
|
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__``.
|
|
|
|
|
|
.. _custom-comparison:
|
|
|
|
Customization
|
|
-------------
|
|
|
|
As with other features, you can exclude fields from being involved in comparison operations:
|
|
|
|
.. doctest::
|
|
|
|
>>> from attr 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 `sorted`:
|
|
|
|
.. doctest::
|
|
|
|
>>> from attr import define, field
|
|
|
|
>>> @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 <https://github.com/python-attrs/attrs/issues/435>`_.
|
|
|
|
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(order=False)
|
|
class C:
|
|
an_array = field(eq=attr.cmp_using(eq=numpy.array_equal))
|
|
|
|
|
|
.. warning::
|
|
|
|
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.
|