Python中的可比较类3 [英] Comparable classes in Python 3

问题描述

在Python 3中使类可比的标准方法是什么？ （例如，通过id。）

What is the standard way of making a class comparable in Python 3? (For example, by id.)

推荐答案

对于一整套比较函数，我使用了下面的mixin，你可以

For a full set of comparison functions I have used the following mixin, which you could put in say for example a mixin.py in your module.

class ComparableMixin(object):
    def _compare(self, other, method):
        try:
            return method(self._cmpkey(), other._cmpkey())
        except (AttributeError, TypeError):
            # _cmpkey not implemented, or return different type,
            # so I can't compare with "other".
            return NotImplemented

    def __lt__(self, other):
        return self._compare(other, lambda s, o: s < o)

    def __le__(self, other):
        return self._compare(other, lambda s, o: s <= o)

    def __eq__(self, other):
        return self._compare(other, lambda s, o: s == o)

    def __ge__(self, other):
        return self._compare(other, lambda s, o: s >= o)

    def __gt__(self, other):
        return self._compare(other, lambda s, o: s > o)

    def __ne__(self, other):
        return self._compare(other, lambda s, o: s != o)

要使用上面的mixin，你需要实现一个_cmpkey（）方法，返回一个可以比较的对象的键，类似于排序时使用的key（）函数。实施方式如下：

To use the mixin above you need to implement a _cmpkey() method that returns a key of objects that can be compared, similar to the key() function used when sorting. The implementation could look like this:

>>> from .mixin import ComparableMixin

>>> class Orderable(ComparableMixin):
...
...     def __init__(self, firstname, lastname):
...         self.first = firstname
...         self.last = lastname
...
...     def _cmpkey(self):
...         return (self.last, self.first)
...
...     def __repr__(self):
...         return "%s %s" % (self.first, self.last)
...
>>> sorted([Orderable('Donald', 'Duck'), 
...         Orderable('Paul', 'Anka')])
[Paul Anka, Donald Duck]

我使用这个而不是total_ordering配方的原因是此错误。它在Python 3.4中是固定的，但通常你还需要支持旧的Python版本。

The reason I use this instead of the total_ordering recipe is this bug. It's fixed in Python 3.4, but often you need to support older Python versions as well.

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