Py3.0 transition aid. The sorted() builtin and the list.sort() method no longer accept a cmp function in Python 3.0. Most cases are easy to convert manually. This recipe handles the remaining cases.
Python, 18 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 | def cmp_to_key(mycmp):
'Convert a cmp= function into a key= function'
class K(object):
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
return K
|
In most cases it is easy to convert old-style to new-style. For instance, l.sort(cmp=lambda x, y: cmp(x.lower(), y.lower) converts directly to l.sort(key=str.lower).
However, sometimes there are extensive existing tests that supply custom cmp functions or a user supplied cmp function (part of the exposed API). In those cases, this wrapper can ease the transition. For instance, l.sort(cmp=mycmp) converts to l.sort(key=cmp_to_key(mycmp)).
The functions above was added to Python 2.7 and Python3.2 in the functools module.
Tags: 2_to_3
Warning: the cmp function may return any integer, not just 0, 1, -1. What matters is whether it is greater than, lower than, or equal to 0.
__lt__should be written as:and so on.
See note (8) at http://docs.python.org/library/stdtypes.html#mutable-sequence-types