Rock Paper Scisccors with deques

rps.py

import collections

def rps(*choices):
    """choices must be in order so that each proceeding element defeats its neighbor.
    
    Returns a function that takes two members of choices and decides which one would win in that RPS game.
    
    rps("rock", "paper", "scissors") or rps("paper", "scissors", "rock"), but never rps("scissors", "paper", "rock")
    """
    
    assert len(choices) % 2 == 1, "Length of choices should always be odd."
    matrix = collections.deque(choices)
    midpoint = len(choices) // 2
    
    def who_wins(a, b):
        if a==b:
            return "Tie."
        rotate_length = midpoint - matrix.index(a)
        matrix.rotate(rotate_length)  # a is now in the middle
        b_index = matrix.index(b)     # so we know that...
        if midpoint < b_index:
            return f"{b} beats {a}"
        else:
            return f"{a} beats {b}"
       
    return who_wins

def main():
    game = rps("rock", "paper", "scissors")
    result = game("scissors", "rock")
    print(result)

if __name__ == "__main__":
    main()