子类没有正确地从超类继承结构

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 class 继承时遇到问题，尽管我经常使用本教程我一直在关注，我还没有在 Stack Overflow 上看到其他人遇到过这个问题。这是代码（别担心，没什么太复杂的）：

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

在解释时直译为：

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

不管它在哪里被调用，或者是谁调用了 __init__，前缀 _Animal 都会出现，因为它实际位于 Animal class 之下.

但是当你在这里使用这些属性时，因为它物理上位于 Dog class 下面，所以得到的名字被改成了这样：

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)

其中 Dog 对象肯定没有名为 self._Dog__name 的属性，而是具有 self._Animal__name.

属性

子类没有正确地从超类继承结构

Subclass not inheriting structure from superclass properly

python

name-mangling