What does this do?

gen.py

import random
import string
import re


allowable = re.sub(r'[IO10]', '', (string.ascii_uppercase + string.digits))


def combos(place):
    for char in allowable:
        if place == 1:
            yield char
        else:
            for subchar in combos(place - 1):
                yield char + subchar

four_digit_combos = combos(4)
enough_for_1000_people = random.sample(list(four_digit_combos), 1000)

print(enough_for_1000_people)