Hướng dẫn dùng comparable python python

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 __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]

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]

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.