47 lines
1.5 KiB
ReStructuredText
47 lines
1.5 KiB
ReStructuredText
Comparison
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==========
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By default, two instances of ``attrs`` classes are equal if all their fields are equal.
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For that, ``attrs`` writes ``__eq__`` and ``__ne__`` methods for you.
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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__``.
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Customization
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-------------
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As with other features, you can exclude fields from being involved in comparison operations:
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.. doctest::
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>>> import attr
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>>> @attr.s
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... class C(object):
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... x = attr.ib()
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... y = attr.ib(eq=False)
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>>> C(1, 2) == C(1, 3)
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True
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Additionally you can also pass a *callable* instead of a bool to both *eq* and *order*.
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It is then used as a key function like you may know from `sorted`:
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.. doctest::
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>>> import attr
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>>> @attr.s
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... class S(object):
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... x = attr.ib(eq=str.lower)
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>>> S("foo") == S("FOO")
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True
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>>> @attr.s
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... class C(object):
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... x = attr.ib(order=int)
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>>> C("10") > C("2")
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True
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This is especially useful when you have fields with objects that have atypical comparison properties.
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Common examples of such objects are `NumPy arrays <https://github.com/python-attrs/attrs/issues/435>`_.
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Please note that *eq* and *order* are set *independently*, because *order* is `False` by default in `modern APIs <next-gen>`.
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You can set both at once by using the *cmp* argument that we've undeprecated just for this use-case.
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