Question

我刚刚开始使用Python，但我无法弄清楚为什么我遇到这样简单的类继承问题，尽管我一直在使用该教程的常用，但我还没有见过任何人Stack Overflow上的其他问题遇到此问题。这是代码（不用担心，没有太复杂）：

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

调用它的位置或调用__init__的人无关紧要，前缀_Animal将会发生，因为它实际位于Animal类之下。

但是当你在这里使用这些属性时，因为它实际上位于Dog类下面，所以这个名字被误解为：

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

子类不能正确地从超类继承结构

1 个答案: