match.py

class User():
    def __init__(self, has=[], wants=[]):
        self.has = has
        self.wants = wants
        self.score = 0

def find_best_match(users=[], user=None):
    best = users[0]
    for u in users:
        for w in user.wants:
            if w in u.has:
                u.score += 1
        #This user has all the wanted items
        if u.score == len(user.wants):
            return u
        elif u.score > best.score:
            best = u
        else:
            pass

    return best

users = []
user1 = User(has=["A", "C"], wants=["B", "D"])
users.append(user1)
user2 = User(has=["D"], wants=["A"])
users.append(user2)
user3 = User(has=["A", "B", "D"], wants="C")
users.append(user3)

best_match = find_best_match(users=users, user=user1)

print best_match.score, best_match.has