Python infinite product generator
Well, you effectively have 3 nested loops including the generator comprehension, which you can reduce to two just by simplifying:

def get_products(string):
    for i in itertools.count(0):
        for product in itertools.product(string, repeat=i):
            yield product


Or if you are intent on putting it in a single line, use chain:

products_generator = itertools.chain.from_iterable(itertools.product("ABC", repeat=i)
                                                   for i in itertools.count(0))