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Hi, quiver. I don't think we can easily go around this problem 
if we have to capture iterators in generator expression.
If you run following, you'll know what I mean.

>>> a = iter("abcd")
>>> b = iter("abcd")
>>> [(x, y) for x in a for y in b]
[('a', 'a'), ('a', 'b'), ('a', 'c'), ('a', 'd')]

I think one possible solution could be, instead of passing 
evaluations of iterators in generator expression,  make a list 
from iterator and, then pass it as argument. For instance,

g = (x for x in iter("abcd"))

will be equivalent to,

def __gen(_[1]):
    for x in _[1]:
        yield x
g = __gen(list(iter("abcd"))) # see 'list'

- instead of g = __gen(iter("abcd"))  .

I'm not sure if I'm in a position to decide to do that way or 
not. If the current reviewer (rhettinger) approves it, I'll do 
that way. Or else, I think I will post it on the mailing list.