子类没有正确地从超类继承结构[重复]

Question

我刚开始使用 Python，但我无法弄清楚为什么我在使用如此简单的类继承时会遇到问题，尽管我一直在关注本教程的常见用法，但我还没有看到任何人其他在 Stack Overflow 上遇到此问题。这是代码（别担心，没什么复杂的）：

import random
import sys
import os

class Animal:
    __name = ""
    __height = 0
    __weight = 0
    __sound = 0

    def __init__(self, name, height, weight, sound):
        self.__name = name
        self.__height = height
        self.__weight = weight
        self.__sound = sound

    def toString(self):
        return "{} is {} cm tall and {} kilograms and says {}".format(self.__name,
                                                                      self.__height,
                                                                      self.__weight,
                                                                      self.__sound)

cat = Animal ('Whiskers', 33, 10, 'meow')
print(cat.toString())

bird = Animal ('Flutie', 33, 10, 'tweet')
print(bird.toString())

class Dog(Animal):

    def __init__(self, name, height, weight, sound):
        super(Dog, self).__init__(name, height, weight, sound)

    def toString(self):
        return "{} is {} cm tall and {} kilograms and says {}".format(self.__name,
                                                                      self.__height,
                                                                      self.__weight,
                                                                      self.__sound)

spot = Dog ('Spot', 53, 27, "Woof")

print(spot.toString())

...这是输出：

Whiskers is 33 cm tall and 10 kilograms and says meow
Flutie is 33 cm tall and 10 kilograms and says tweet
Traceback (most recent call last):
  File "C:/.../animal_test.py", line 72, in <module>
    print(spot.toString())
  File "C:/.../animal_test.py", line 65, in toString
    return "{} is {} cm tall and {} kilograms and says {}".format(self.__name,
AttributeError: 'Dog' object has no attribute '_Dog__name'

Answer 1

双下划线代表name mangling。

class Animal:
    def __init__(self, name, height, weight, sound):
        self.__name = name
        self.__height = height
        self.__weight = weight
        self.__sound = sound

解释时直译为：

class Animal:
    def __init__(self, name, height, weight, sound):
        self._Animal__name = name
        self._Animal__height = height
        self._Animal__weight = weight
        self._Animal__sound = sound

无论在哪里调用，或者是谁调用了__init__，前缀_Animal 都会出现，因为它实际上位于Animal 类下。

但是当你在这里使用属性时，因为它物理上位于 Dog 类下，所以得到的名称会变成这样：

class Dog(Animal):

    def __init__(self, name, height, weight, sound):
        super(Dog, self).__init__(name, height, weight, sound)

    def toString(self):
        return "{} is {} cm tall and {} kilograms and says {}".format(self._Dog__name,
                                                                      self._Dog__height,
                                                                      self._Dog__weight,
                                                                      self._Dog__sound)

Dog 对象肯定没有self._Dog__name 的属性，而是有self._Animal__name 的属性。