Christmas gift exchange

gifting

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from random import sample

# people grouped together cannot gift to each other
people = [
    ('Sue', 'Sam'),
    ('Heather', 'Matt'),
    ('Noelle', 'George'),
]

gifters = set([p for group in people for p in group])


def my_group(person):
    for group in people:
        if person in group:
            return group


def gifter_for(person, pairs):
    for k, v in pairs.items():
        if v == person:
            return k
    return None


def remaining_recipients(gifter, gifters, pairs):
    group = my_group(gifter)
    possible_recipients = gifters - set(group) - set(pairs.values())
    giver = gifter_for(gifter, pairs)
    if giver:
        possible_recipients -= {giver}
    return possible_recipients


def pair_up(gifters):
    pairs = {}

    for gifter in gifters:
        possible_recipients = remaining_recipients(gifter, gifters, pairs)
        try:
            recipient = sample(possible_recipients, 1)[0]
        except ValueError:
            pairs = {}
            break
        pairs[gifter] = recipient

    if pairs:
        return pairs
    else:
        print('Try again...')
        pairs = pair_up(gifters)
        return pairs


def main():
    pairs = pair_up(gifters)
    for k, v in pairs.items():
        print("{} → {}".format(k, v))


if __name__ == '__main__':
    main()