testing if an iterator is empty

[Gribouillis]

this needs to work with whatever iterator it gets.

You want something that is structurally impossible. Consider the following iterator

def user_inputs():
    while True:
        yield input("Give me a string: ")

iterator = user_inputs()

Now 'iterator' is empty iff the user decides not to type the Enter key until the program exits. There is no way for the program to read the user's mind. Even if the program calls next(iterator), the answer will be known only if this call returns before the program exits.