matrix.py

import itertools

class World:

    def __init__(self, interactions):
        self.objects = []
        self.interactions = interactions

    def add(self, item):
        self.objects.append(item)

    def tick(self):
        for a, b in itertools.combinations(self.objects, 2):
            self.interactions.interact(world, a, b)

class GameObject:

    def __init__(self, name):
        self.name = name

class Player(GameObject):
    pass

class Shot(GameObject):
    pass

class Monster(GameObject):
    pass

class Interactions:

    def interact(self, world, a, b):
        first, second = sorted([a, b], key=lambda x: x.__class__.__name__.lower())
        name = f"{first.__class__.__name__.lower()}_{second.__class__.__name__.lower()}"
        if hasattr(self, name):
            getattr(self, name)(world, first, second)
        else:
            print(f"interaction {name} not defined")

    def player_shot(self, world, player, shot):
        print(f"player {player.name} vs shot {shot.name}")

    def monster_player(self, world, monster, player):
        print(f"monster {monster.name} vs player {player.name}")

if __name__ == "__main__":
    world = World(Interactions())
    world.add(Player("Mario"))
    world.add(Shot("Ice Bullet"))
    world.add(Monster("Bowser"))
    world.tick()

Prints this:

player Mario vs shot Ice Bullet
monster Bowser vs player Mario
interaction monster_shot not defined