Factorial calculation using Python

The construct could look like this:

while True:
    N = input("Please input factorial you would like to calculate: ")
    try: # try to ...
        N = int(N) # convert it to an integer.
    except ValueError: # If that didn't succeed...
        print("Invalid input: not an integer.")
        continue # retry by restarting the while loop.
    if N > 0: # valid input
        break # then leave the while loop.
    # If we are here, we are about to re-enter the while loop.
    print("Invalid input: not positive.")

In Python 3, input() returns a string. You have to convert it to a number in all cases. Your N != int(N) thus makes no sense, as you cannot compare a string with an int.

Instead, try to convert it to an int directly, and if that doesn't work, let the user enter again. That rejects floating point numbers as well as everything else which is not valid as an integer.