Python Inheritance and Tricks By albro

With the help of inheritance in Python, we can inherit the properties and behaviors of a class from a higher class. For example, the cat class inherits from the animal class so that we don't have to redefine all functions. In this post, I'll talk about inheritance in Python.

In the principles of object-oriented programming, we have a basic discussion called inheritance in classes. With the help of inheritance, the properties and behaviors of a class are inherited from a higher class.

Just as in human reproduction, children inherit properties and behaviors from their parents. Of course, each child can have their own unique properties and behaviors.

To better match inheritance in Python to the real world, I'll give another small example. Suppose we have a class called "Pet" which is our pet.

In this case, we can have subclasses like cat and dog. Both of them are a type of pet that, in addition to having the properties of a pet, also have unique properties and behaviors.

Inheritance in Python

We are all familiar with class definition in Python. To make a class inherit from another class, we use parentheses in front of the class name.

Suppose we have two classes A and B. We want B to inherit from A, that is, to have all its properties and methods in itself. For this, we will have a structure similar to the following:

class A:
    pass   # class A body

class B(A):
    pass   # class B body

An example of Python inheritance

Let's go back to the last example I gave. First, we consider a class called Pet for a pet in Python. In the constructor of this class, we define the name, color and age of the pet. We also have two methods:

• The getName() method returns its name.
• The makeSound() method generally prints an irrelevant text. It is clear that the sound of a cat and a dog is different. Later we will learn to redefine these methods for each class.

class Pet:
    def __init__(self, name, color, age):
        self.name = name
        self.color = color
        self.age = age

    def getName(self):
        return self.name

    def makeSound(self):
        print("bla bla bla")

In very simple language, a method is a function that is defined in a class and will be available through the objects of that class.

Now I define the Cat class. I also define a simple method to determine if the cat is chasing the rat:

class Cat(Pet):
    def chasingRat(self):
        print("It's chasing rat!")

Now I make an instance (object) of cat:

kitty = Cat("Kitty", "white", 2)

With the help of the IDE, I check what methods and properties I have access to on this object:

As you can see, I can use the methods and properties of both the Pet class and the Cat class. This means inheritance in Python! 🙂

If you pay attention, the constructor of the parent class was also used when creating the cat. In the following code, I access its various methods:

print(kitty.getName())  # Kitty
kitty.chasingRat()  # It's chasing rat!

Rewrite in child class

When we want to rewrite a method of the parent class in the child class, it is called Method Overriding. I want to override the makeSound() method in the Cat class and change its body.

class Cat(Pet):
    def chasingRat(self):
        print("It's chasing rat!")

    def makeSound(self):
        print("meowwww!")

Now if we create an object from the Cat class and call makeSound(), the method inside the Cat class will be executed. In this way, we were able to rewrite the method during inheritance in Python.

kitty = Cat("Kitty", "white", 2)
kitty.makeSound()

Important points of inheritance in Python

You see that we were able to inherit between two classes so easily. It is better to review 2 very important points:

Multiple inheritance in Python

Python supports multiple inheritance. It means that each class can inherit from two or more other classes at the same time.

For multiple inheritance in Python, it is enough to separate the names of the parent classes with a comma (,) and do the same as before:

class A:
    # body

class B:
    # body

class C(A, B):
    # body of C that inherited from A, B

Note that the order of these classes is important. If there are several methods with the same name in these classes, the method on the rightmost side of the class will be overridden.

Hierarchical inheritance

You've probably guessed by now that we can have sequential inheritance in Python classes. If we take the original example of the post, the pet itself inherits from the Animal class. Therefore, we can have a structure similar to the following.

class Animal:
    pass

class Pet(Animal):
    pass

class Cat(Pet):
    pass

In order not to make the codes long, I've removed the body of the classes and used the pass keyword.

Parent class in Python inheritance

Sometimes it is necessary to access the methods of the parent class in the child class. We have two methods for this:

1. Using the super() function to access the parent class
2. Using the name of the parent class and accessing its methods

Let's say I want to get the cat's eye color in the Cat constructor as well. For this I can rewrite the whole body; It means to re-initialize all the variables. I can also get help from the Pet constructor, similar to the following code:

class Pet:
    def __init__(self, name, color, age):
        self.name = name
        self.color = color
        self.age = age

class Cat(Pet):
    def __init__(self, name, color, age, eye_color):
        super().__init__(name, color, age)
        self.eye_color = eye_color


kitty = Cat("Kitty", "white", 2, "black")

If we want to do the second method, the child class will change to the following state. Note that in this method, we have to give self as an input argument to the method we called.

class Cat(Pet):
    def __init__(self, name, color, age, eye_color):
        Pet.__init__(self, name, color, age)
        self.eye_color = eye_color

Suggestion: If the class only inherits from one class, use super() and in multiple inheritance in Python, use the names of the classes.