Outerzip / zip longest function (with multiple fill values)

It's called izip_longest (zip_longest in python-3.x):

>>> from itertools import zip_longest
>>> a = [1,2,3]
>>> b = [4,5,6,7]
>>> list(zip_longest(a, b, fillvalue=0))
[(1, 4), (2, 5), (3, 6), (0, 7)]

You could modify zip_longest to support your use case for general iterables.

from itertools import chain, repeat

class OuterZipStopIteration(Exception):
    pass

def outer_zip(*args):
    count = len(args) - 1

    def sentinel(default):
        nonlocal count
        if not count:
            raise OuterZipStopIteration
        count -= 1
        yield default

    iters = [chain(p, sentinel(default), repeat(default)) for p, default in args]
    try:
        while iters:
            yield tuple(map(next, iters))
    except OuterZipStopIteration:
        pass


print(list(outer_zip( ("abcd", '!'), 
                      ("ef", '@'), 
                      (map(int, '345'), '$') )))