typing - 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 in Python?

My first reaction is to do something like this:

def isInteger(n):
    return int(n) == n

But I can't help thinking that this is 1) expensive 2) ugly and 3) subject to the tender mercies of machine epsilon.

Does Python provide any native means of type checking variables? Or is this considered to be a violation of the language's dynamically typed design?

EDIT: since a number of people have asked - the application in question works with IPv4 prefixes, sourcing data from flat text files. If any input is parsed into a float, that record should be viewed as malformed and ignored.

Answer 1

isinstance(n, int)

If you need to know whether it's definitely an actual int and not a subclass of int (generally you shouldn't need to do this):

type(n) is int

this:

return int(n) == n

isn't such a good idea, as cross-type comparisons can be true - notably int(3.0)==3.0