python - Python 中的多重继承

Question

我正在开始学习 Python 语言，需要对我的代码进行评论以及对我收到的错误消息的解决方案。

代码创建了一个有两个祖先的 Robot 类；变形金刚和高达。第三类 Hybrid 继承自这些。我可以毫无错误地实例化一个变形金刚和一个高达。实例化 Hybrid 会返回错误。代码和错误如下:

主.py

from multiple_inheritance import Robot, Transformer, Gundam, Hybrid

tito = Gundam("Tito", "Japan")
optimus = Transformer("Optimus Prime", "Mars")
Jaeger = Hybrid("Striker", "US")

print(tito)
print(optimus)

多重继承

class Robot(object):
    """A robot class"""
    def __init__(self, name):
            self.name = name

    def __str__(self):
            return "{name}".format(name = self.name)

class Transformer(Robot):
    """A transformer"""
    def __init__(self, name, planet):
            self.planet = planet
            super(Transformer, self).__init__(name)

    def __str__(self):
            return "Name = {name}, Planet = {planet}".\
                   format(name = self.name, planet = self.planet)

class Gundam(Robot):
    """A Gundam"""
    def __init__(self, name, country):
            self.country = country
            super(Gundam, self).__init__(name)

    def __str__(self):
            return "Name = {name}, Country = {country}".\
                   format(name = self.name, country = self.country)

class Hybrid(Transformer, Gundam):
    """Ultimate Robot"""

错误信息

Traceback (most recent call last):
  File "D:\Tech\Python\my_code\unit10\multiple_inheritance_main.py", line 5, in <module>
    Jaeger = Hybrid("Striker", "US")
  File "D:\Tech\Python\my_code\unit10\multiple_inheritance.py", line 13, in __init__
    super(Transformer, self).__init__(name)
TypeError: __init__() missing 1 required positional argument: 'country'

Answer 1

Hybrid 的 mro 看起来像这样:

>>> Hybrid.__mro__
(<class '__main__.Hybrid'>, <class '__main__.Transformer'>, <class '__main__.Gundam'>, <class '__main__.Robot'>, <type 'object'>)

如您所见，在 Transformer 之后，下一个类是 Gundam，当从 Transformer 的 __init__ 调用它时，您没有传递足够的参数给它>:

class Transformer(Robot):
    """A transformer"""
    def __init__(self, name, planet):
            self.planet = planet
            #####This calls Gundam's __init__
            super(Transformer, self).__init__(name)

所以，重点是 super() 调用 MRO 中的下一个类，而不是如您预期的那样调用 Transformer 的基类。

---

与 super() 相关的非常好的帖子:Python’s super() considered super!