The documentation (eg at http://docs.python.org/release/2.6.5/library/functions.html#filter) tells that there should be an itertools.filterfalse() function complementary to builtin filter() function, that returns the list of elements (instead of the iterator over them, as ifilterfalse() does), for which the condition is failed. This function is absent from Python 2.x branch (though obviously is present in 3.x, as all the i* functions are renamed to their non-i* counterparts).