Why is my python for loop stopping after 3 iterations?

March 6, 2024

I am trying to write a Secret Santa type of program. The function takes in a list of names as a parameter and is supposed to match each person with another person. No one can be matched with themselves, and each person can only receive and give one gift. It is a simple program so I’ll include the entire thing.

import random

Game1 = ["Alice", "Bob", "Charlie", "David", "Eve", "Frank"]

def matchPeople(players):
    needGift = players
    matches = []

    for player in players:
        def getReceiver():
            receiver = random.choice(needGift)
            if receiver == player:
                getReceiver()
            else: 
                matches.append([player, receiver])
                needGift.remove(receiver)
        getReceiver()
    print(matches)

matchPeople(Game1)

It is running as expected (I think), except it is stopping after 3 iterations. Upon running the matchPeople() function this is the outcome. I am very new to python (coming from JS), so I’m sure there is a logical explanation. However! I do not know what it is…

[['Alice', 'Charlie'], 
 ['Bob', 'David'], 
 ['Eve', 'Bob']]

>Solution :

Your problem here is that needGift and players refer to the same object in memory – and when you remove elements from it inside your nested function, they are also removed from the player list.

The change listed bellow will make needGift a copy of the players list (by taking a "slice" starting at the begging and proceeding to the end of it – the default slice values when you suppress the indexes around the :)

change

needGift = players

needGift = players[:]