itertools.imap and map in Python 2.7 produces inconsistent behaviour when mapping the null (None) function over multiple sequences.
 


>>> [a for a in map(None, list("abcd"), range(3))]
[('a', 0), ('b', 1), ('c', 2), ('d', None)]
>>> from itertools import imap
>>> [a for a in imap(None, list("abcd"), range(3))]
[('a', 0), ('b', 1), ('c', 2)]
>>> [a for a in map(None, list("abcd"), range(3))] == [a for a in imap(None, list("abcd"), range(3))]
False
>>> 



This inconsistent and unintuitive behvaiour caused a bug in my program

This is a documented behavior difference in itertools.imap:

"If function is set to None, then imap() returns the arguments as a tuple. Like map() but stops when the shortest iterable is exhausted instead of filling in None for shorter iterables. The reason for the difference is that infinite iterator arguments are typically an error for map() (because the output is fully evaluated) but represent a common and useful way of supplying arguments to imap()." 

https://docs.python.org/2/library/itertools.html#itertools.imap

Also note that the behavior of map() in Python 3 has been changed to also stop with the termination of the shortest iterator.

https://docs.python.org/3.4/whatsnew/3.0.html#views-and-iterators-instead-of-lists