#Python Inheritance

Inheritance allows us to define a class that inherits all the methods and properties from another class.

• Parent class is the class being inherited from, also called the base class.
• Child class is the class that inherits from another class, also called the derived class.

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#Create a Parent Class

Any class can be a parent class, so the syntax is the same as creating any other class.

Example: Create a class named Person, with firstname and lastname properties, and a printname method:

pythoncopyclass Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

# Use the Person class to create an object, and then execute the printname method:
x = Person("John", "Doe")
x.printname()

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#Create a Child Class

To create a class that inherits the functionality from another class, send the parent class as a parameter when creating the child class.

Example: Create a class named Student, which will inherit the properties and methods from the Person class:

pythoncopyclass Student(Person):
  pass

Note: Use the pass keyword when you do not want to add any other properties or methods to the class.

Now the Student class has the same properties and methods as the Person class.

Example: Use the Student class to create an object, and then execute the printname method:

pythoncopyx = Student("Mike", "Olsen")
x.printname()

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#Add the init() Function

So far we have created a child class that inherits the properties and methods from its parent. We want to add the init() function to the child class (instead of the pass keyword).

Note: The init() function is called automatically every time the class is being used to create a new object.

Example: Add the init() function to the Student class:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname):
    # add properties etc.

When you add the init() function, the child class will no longer inherit the parent's init() function. The child's init() function overrides the inheritance of the parent's init() function.

To keep the inheritance of the parent's init() function, add a call to the parent's init() function:

Example:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname):
    Person.__init__(self, fname, lname)

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#Use the super() Function

Python also has a super() function that will make the child class inherit all the methods and properties from its parent:

Example:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)

By using the super() function, you do not have to use the name of the parent element; it will automatically inherit the methods and properties from its parent.

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#Add Properties

Example: Add a property called graduationyear to the Student class:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)
    self.graduationyear = 2019

To make the year dynamic, add another parameter to the init() function:

Example:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

x = Student("Mike", "Olsen", 2019)

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#Add Methods

Example: Add a method called welcome to the Student class:

pythoncopyclass Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

  def welcome(self):
    print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

Important: If you add a method in the child class with the same name as a function in the parent class, the inheritance of the parent method will be overridden.