The following code in six fails to type check:

try:
    advance_iterator = next
except NameError:
    def advance_iterator(it):
        return it.next()
next = advance_iterator

.../lib/python3.4/site-packages/six.py, line 501: Name 'advance_iterator' already defined

But advance_iterator can't be already defined: for NameError to be thrown, the lookup of next must have failed.

Whats the right way to handle this? Just mask it?