Python class not inheriting properties from its parent

I am new to the Python programming language, and I am working my way through a tutorial on object-oriented programming in Python.  The purpose of the lesson is to learn the important topic of inheritance of classes.  (Here's a shoutout to Derek, who is hosting this excellent tutorial: https://www.youtube.com/watch?v=N4mEzFDjqtA.)

Having created a class called Animal, I then create a new class called Dog, based on Animal.  The program is giving me the error that the Dog class does not recognize the variables inherited from the super class Animal.  Following is my code, and this is my error: "AttributeError: 'Dog' object has no attribute '_Dog__Name'", which comes within Dog.toString() (lines 67-68).   My assumption is that the class definition, "class Dog(Animal):", defines Dog as inheriting attributes from Animal, and Derek's code worked when ran as written here.  Is there something I'm missing?

import random
import sys
import os

#Object-oriented programming
class Animal:
    __Name = None
    __Height = 0
    __Weight = 0
    __Sound = 0

    def set_name(self, name):
        self.__Name = name

    def get_name(self):
        return self.__Name

    def set_height(self, height):
        self.__Height = height

    def get_height(self):
        return self.__Height

    def set_weight(self, weight):
        self.__Weight = weight

    def get_weight(self):
        return self.__Weight

    def set_sound(self, sound):
        self.__Sound = sound

    def get_sound(self):
        return self.__Sound

    def __init__(self, name, height, weight, sound):
        self.__Name = name
        self.__Height = height
        self.__Weight = weight
        self.__Sound = sound

    def get_type(self):
        print ("Animal")

    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())

class Dog(Animal):
    __Owner = ""

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

    def set_owner(self, owner):
        self.__Owner = owner

    def get_owner(self):
        return self.__Owner

    def get_type(self):
        print("Dog")
    def toString(self):
        return "{} is {} cm tall and {} kilograms and says {}.  His owner is {}".format(self.__Name, self.__Height, self.__Weight, self.__Sound, self.__Owner)
    def multiple_sounds(self, how_many=None):
        if (how_many is None):
            print(self.get_sound())
        else:
            print(self.get_sound() * how_many)



spot = Dog("Spot", 53, 27, "Ruff", "Derek")
print(spot.toString)

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