The following mixin implements the full suite of rich comparison operators if __cmp__ is defined. See http://docs.python.org/ref/customization.html
Python, 23 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | class RichCmpMixin(object):
"""
Define __cmp__, and inherit from this class to provide full rich
comparisons.
"""
def __eq__(self, other):
return self.__cmp__(other)==0
def __ne__(self, other):
return self.__cmp__(other)!=0
def __lt__(self, other):
return self.__cmp__(other)==-1
def __le__(self, other):
return self.__cmp__(other)!=1
def __gt__(self, other):
return self.__cmp__(other)==1
def __ge__(self, other):
return self.__cmp__(other)!=-1
|
The __cmp__ method is sufficient to provide comparisons between user-defined classes. However, inheriting from a base class (such as a builtin) which already provides the rich-comparison methods will cause the derrived __cmp__ not to be used.
Probably needs testing.
Tags: oop
__cmp__ can return other values. The return values from __cmp__ are negative (less than), 0 (equals) or positive (greater than).
You therefore can't just compare with -1, 0 and 1 - you need to check < 0, 0 and > 0.
Sorry, why would you want this? If you define __cmp__, you can already use your object with <, >, !=, etc. so you shouldn't need any of the rich comparisons defined.
A more useful mixin would be one that defines all the rich comparisons if you just define __eq__ and __lt__. (Python doesn't fill in the missing comparison operators because for some types you can't assume that
not <implies>=.)Good question. I don't remember why I wrote this.
@steven: My understanding is that __cmp__ is going away in Python 3. I think it is gone as of Python 3.0.1.