Function that returns a tuple gives TypeError: 'NoneType' object is not iterable

Question

What does this error mean? I'm trying to make a function that returns a tuple. I'm sure i'm doing all wrong. Any help is appreciated.

from random import randint
A = randint(1,3)
B = randint(1,3)
def make_them_different(a,b):
    while a == b:
        a = randint(1,3)
        b = randint(1,3)
        return (a,b)
new_A, new_B = make_them_different(A,B)

Answer 1

Your code returns None if a != b.

Since, you have the return statement inside the while loop, if the while loop never gets executed, Python returns the default value of None which cannot be assigned to new_A, new_B.

>>> print make_them_different(2, 3)
None

>>> print make_them_different(2, 2)
(2, 1)

You could fix this by returning the default values (since they are different and that's what you intend to do)

def make_them_different(a,b):
    while a == b:
        a = randint(1,3)
        b = randint(1,3)
    return (a,b)  # Dedented the return line.

Demo -

>>> make_them_different(2, 2)
(3, 2)
>>> make_them_different(2, 3)
(2, 3)

Answer 2

Indent the return one level lower:

from random import randint
A = randint(1,3)
B = randint(1,3)
def make_them_different(a,b):
    while a == b:
        a = randint(1,3)
        b = randint(1,3)
    return (a,b)
new_A, new_B = make_them_different(A,B)

Otherwise a,b will be regenerated only once - they may collide again after that, since you're never looping.