[orblivion]

> I'm surprised by the comment that Python 3 removed cmp. Perhaps that's a temporary omission.

Guido and company insist that you can (almost?) always find a way supplying a key function. For better or worse, they decided it was the best way, and going by the Python philosophy they removed anything that isn't the one obvious right way to do it. Perhaps it's available in a library somehow, that's what they did to other things that are unnecessary or useful 99% of the time but may still be 1% of the time.

Similarly, Guido once almost removed lambda, but he faced an insurrection.

[jasomill]

From the Python 3.2 standard library functools.py:

    def cmp_to_key(mycmp):
        """Convert a cmp= function into a key= function"""
        class K(object):
            __slots__ = ['obj']
            def __init__(self, obj, *args):
                self.obj = obj
            def __lt__(self, other):
                return mycmp(self.obj, other.obj) < 0
            def __gt__(self, other):
                return mycmp(self.obj, other.obj) > 0
            def __eq__(self, other):
                return mycmp(self.obj, other.obj) == 0
            def __le__(self, other):
                return mycmp(self.obj, other.obj) <= 0
            def __ge__(self, other):
                return mycmp(self.obj, other.obj) >= 0
            def __ne__(self, other):
                return mycmp(self.obj, other.obj) != 0
            __hash__ = None
        return K