secret_santa.py

from random import randrange

N = 5

has_santa = set()
is_santa = set()
pairs = set()

while len(has_santa) < N:

    santa_to_try = randrange(N)
    while santa_to_try in is_santa:
        santa_to_try = randrange(N)
    is_santa.add(santa_to_try)

    santee_to_try = randrange(N)
    while santee_to_try in has_santa or santa_to_try == santee_to_try:
        santee_to_try = randrange(N)
    has_santa.add(santee_to_try)

    pairs.add((santa_to_try, santee_to_try))

print(pairs)