在Python中处理钻石继承超类调用

Question

我的课程设置如下所示

from abc import abstractmethod


class Player:
    def __init__(self, name, age):
        self._player_name = name
        self._age = age

    @property
    def player_name(self):
        return self._player_name

    @property
    def age(self):
        return self._age

    @abstractmethod
    def _prefix(self) -> str:
        pass

    @abstractmethod
    def _suffix(self) -> str:
        pass

    def pretty_print(self) -> str:
        return f"{self.player_name} is a {self._prefix()} and is {self.age} years old. Accomplishments: {self._suffix()}"


class Footballer(Player):
    def __init__(self, name, age, goals_scored):
        super().__init__(name, age)
        self._goals_scored = goals_scored

    @property
    def goals_scored(self):
        return self._goals_scored

    def _prefix(self) -> str:
        return "Football Player"

    def _suffix(self) -> str:
        return f"Goals Scored {self._goals_scored}"


class CarRacer(Player):
    def __init__(self, name, age, races_won, laps):
        super().__init__(name, age)
        self._races_won = races_won
        self._laps = laps

    @property
    def laps(self):
        return self._laps

    @property
    def races_won(self):
        return self._races_won

    def _prefix(self) -> str:
        return "Formula 1 racer"

    def _suffix(self) -> str:
        return f"Races won: {self.races_won}, Laps count: {self.laps}"


class AllRounder(Footballer, CarRacer):
    def __init__(self, name, age, goals_scored, races_won, laps):
        super().__init__(name, age, goals_scored)
        super(CarRacer, self).__init__(name, age, races_won, laps)

    def _prefix(self) -> str:
        return "All Rounder"

    def _suffix(self) -> str:
        return f"{Footballer._prefix(self)}, {CarRacer._prefix(self)}"

现在在我的主要方法中，我正在执行以下操作：

if __name__ == '__main__':
    all_rounder = AllRounder("Jack", 30, 150, 200, 1000)
    print(all_rounder.pretty_print())

当实例化开始时，我不断遇到以下错误

Traceback (most recent call last):
  File "/Users/kmahadevan/githome/playground/python_projects/playground/pythonProject/oops/diamond_inheritance.py", line 79, in <module>
    all_rounder = AllRounder("Jack", 30, 150, 200, 1000)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/kmahadevan/githome/playground/python_projects/playground/pythonProject/oops/diamond_inheritance.py", line 68, in __init__
    super().__init__(name, age, goals_scored)
  File "/Users/kmahadevan/githome/playground/python_projects/playground/pythonProject/oops/diamond_inheritance.py", line 31, in __init__
    super().__init__(name, age)
TypeError: CarRacer.__init__() missing 2 required positional arguments: 'races_won' and 'laps'

我不完全确定应该如何调用

__init__

中的

AllRounder

方法以便调用两个基类。

类层次结构的图形表示，以便更好地理解

Answer 1

当一个类从多个基类继承时，Python 会线性化继承树。可以通过在任何类上查找

<className>.__mro__

来访问此类的线性列表。

print(AllRounder.__mro__)

将有以下输出：

(<class '__main__.AllRounder'>, <class '__main__.Footballer'>, <class '__main__.CarRacer'>, <class '__main__.Player'>, <class 'object'>)

在一个类上调用

super()

将导致 Python 在上面的列表中查找下一个类，并调用它的

__init__

。在这种情况下，当

Footballer

调用

super()

时，

CarRacer.__init__

会被调用；不是

Player.__init__

，尽管足球运动员的类别定义是：

class Footballer(Player)

解决此问题的一种方法是让所有

__init__

方法消耗

**kwargs

。类的

__init__

只能声明它实际消耗的那些参数，同时让所有其他参数沿着链向上传递。

如果 **kwargs 有一个与位置参数名称匹配的键，那么 python 会替换该参数的值并从 kwargs 中删除该键。

无关注释：要使

Player

成为抽象基类，它必须从

abc.ABC

派生，这样，如果将

Player

实例化为抽象方法，则会出错。

---

代码：

from abc import ABC, abstractmethod


class Player(ABC):
    def __init__(self, name, age, **kwargs):
        super().__init__(**kwargs)
        self._player_name = name
        self._age = age

    @property
    def player_name(self):
        return self._player_name

    @property
    def age(self):
        return self._age

    @abstractmethod
    def _prefix(self) -> str:
        pass

    @abstractmethod
    def _suffix(self) -> str:
        pass

    def pretty_print(self) -> str:
        return f"{self.player_name} is a {self._prefix()} and is {self.age} years old. Accomplishments: {self._suffix()}"


class Footballer(Player):
    def __init__(self, goals_scored, **kwargs):
        super().__init__(**kwargs)
        self._goals_scored = goals_scored

    @property
    def goals_scored(self):
        return self._goals_scored

    def _prefix(self) -> str:
        return "Football Player"

    def _suffix(self) -> str:
        return f"Goals Scored {self._goals_scored}"


class CarRacer(Player):
    def __init__(self, races_won, laps, **kwargs):
        super().__init__(**kwargs)
        self._races_won = races_won
        self._laps = laps

    @property
    def laps(self):
        return self._laps

    @property
    def races_won(self):
        return self._races_won

    def _prefix(self) -> str:
        return "Formula 1 racer"

    def _suffix(self) -> str:
        return f"Races won: {self.races_won}, Laps count: {self.laps}"


class AllRounder(Footballer, CarRacer):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def _prefix(self) -> str:
        return "All Rounder"

    def _suffix(self) -> str:
        return f"{Footballer._prefix(self)}, {CarRacer._prefix(self)}"


if __name__ == "__main__":

    args = {
        "name": "John Doe",
        "age": 41,
        "goals_scored": 1,
        "races_won": 2,
        "laps": 500
    }

    a = AllRounder(**args)
    print(a.pretty_print())

    print("\n== MRO ==")
    print(AllRounder.__mro__)

---

输出将是：

John Doe is a All Rounder and is 41 years old. Accomplishments: Football Player, Formula 1 racer

== MRO ==
(<class '__main__.AllRounder'>, <class '__main__.Footballer'>, <class '__main__.CarRacer'>, <class '__main__.Player'>, <class 'abc.ABC'>, <class 'object'>)