How can I type-check variables in Python?

Question

I have a Python function that takes a numeric argument that must be an integer in order for it behave correctly. What is the preferred way of verifying this

Answer 1

how about:

def ip(string):
    subs = string.split('.')
    if len(subs) != 4:
        raise ValueError("incorrect input")
    out = tuple(int(v) for v in subs if 0 <= int(v) <= 255)
    if len(out) != 4:
        raise ValueError("incorrect input")
    return out

ofcourse there is the standard isinstance(3, int) function ...