get TypeError: <class 'dict'> is wrong data type

I would like to give some feedback about ... Please help I don't understand why I get that """ TypeError: <class 'dict'> is wrong data type """ from next code: on my PC all seems to work properly

class Warrior:
    def __init__ (self):
        self.health=50
        self.attack_damage=5

    def is_alive(self):
        return self.health>0


class Knight(Warrior):
    def __init__ (self):
        self.health=50
        self.attack_damage=7

    def is_alive(self):
        return self.health>0


def fight(unit_1, unit_2):
    while unit_1.is_alive() and unit_2.is_alive():
        unit_1.health-=unit_2.attack_damage
        unit_2.health-=unit_1.attack_damage
    return unit_1.is_alive() and not unit_2.is_alive()