python - Fix a function returning duplicates over time?

Question

I have a function here that returns a 4 digit string. The problem is that when I run the function like 500 times or more, it starts to return duplicates. How to avoid that?

My Function:

import random
def CreatePass():
    Num = str(random.randint(1000, 9999)
    return Num

Answer 1

Generate a list, shuffle that and pop from it each time the function is called:

import random

def CreatePass(_numbers=[]):
    if not _numbers:
        _numbers[:] = range(1000, 10000)
        random.shuffle(_numbers)              
    return str(_numbers.pop())

Note that this re-generates the _numbers list once you've run out, but then you've used up all 8999 possible numbers and would have to accept repetitions anyway.