homepage

In some situation, itertools.groupby fails to group the objects, and produces several groups with the same key. For example, the following code :
from itertools import *
class P(object):
 def __init__(self, key):
 self.key = key
p1 = P(1)
p2 = P(2)
p3 = P(1)
for key, ps in groupby([p1, p2, p3], lambda p: p.key):
 print "group", key
 for p in ps:
 print " - object", p
Produces the following result :
group 1
 - object <__main__.P object at 0xb73d6acc>
group 2
 - object <__main__.P object at 0xb73d6aec>
group 1
 - object <__main__.P object at 0xb73d6b0c>
While I would expect to have only a single group 1, e.g. something like :
group 1
 - object <__main__.P object at 0xb73d6acc>
 - object <__main__.P object at 0xb73d6b0c>
group 2
 - object <__main__.P object at 0xb73d6aec>
It seems that this bug also affects Python 3 (tested on Python 3.1.2)