Subclass does not inherit structure from superclass
I'm just getting started with Python, but I can't figure out why I have a problem with such simple class inheritance, and despite the general use of the tutorial I'm following, I haven't seen anyone else on Stack Overflow faced this problem. Here is the code (don't worry, nothing complicated):
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())
... And here's the output:
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'
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Double underscores represent the name mangling .
class Animal:
def __init__(self, name, height, weight, sound):
self.__name = name
self.__height = height
self.__weight = weight
self.__sound = sound
Literally translated into this when interpreted:
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
It doesn't matter where it was called or who called it __init__
, the prefix _Animal
will be there because it is physically under the class Animal
.
But when you used the attributes here since you were physically in the class Dog
, the resulting name got distorted:
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)
Which object Dog
definitely doesn't have an attribute named self._Dog__name
, it has an attribute instead self._Animal__name
.
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