TypeError: '<' not supported between instances of 'NoneType' and 'int'

I have looked for an answer in Stack Overflow and found that I should be taking an int(input(prompt)), but that's what I am doing

def main():      while True:vPopSize = validinput("Population Size: ")if vPopSize < 4:print("Value too small, should be > 3")continueelse:breakdef validinput(prompt):while True:try:vPopSize = int(input(prompt))except ValueError:print("Invalid Entry - try again")continueelse:break

This problem also comes up when migrating to Python 3.

In Python 2 comparing an integer to None will "work," such that None is considered less than any integer, even negative ones:

>>> None > 1
False
>>> None < 1
True

In Python 3 such comparisons raise a TypeError:

>>> None > 1
Traceback (most recent call last):File "<stdin>", line 1, in <module>
TypeError: '>' not supported between instances of 'NoneType' and 'int'>>> None < 1
Traceback (most recent call last):File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'NoneType' and 'int'