Digits Multiplication, I can't fix assertion error

Here's my code

def checkio(number: int) -> int:
    s = str(number)
    lst = []   
    b = 1
    for x in s:
        y = int(x)
        if y == 0:
            continue
        b = b * y

    return print (b)

When i'm using def. like checkio(1234,)checkio(3456) on python this code works okay but when i hit check, result always stuck at first assert line