Python Inheritance

A class can inherit the attributes of a super-class. This is one of the features of object-oriented programming, where a more specialized class can be defined that uses the attributes (functions and variables) of a super-class and extends the behavior of the super-class. By using a super-class, you can avoid repeating common attributes of "like" classes but also add or override behaviors of the super-class. It also common to use the term "derived" - in the example below, Student and Teacher are derived from Person.

In this example, Person is the super-class and contains the first and last name variables which are common information about Teacher and Student.

Example

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

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

class Student(Person):
    def __init__(self, fname, lname, grade):
        Person.__init__(self, fname, lname)
        self.grade = grade

    def info(self):
        print(self.firstname, self.lastname, 'has a grade of', self.grade)

class Teacher(Person):
    def __init__(self, fname, lname, course):
        Person.__init__(self, fname, lname)
        self.course = course

    def info(self):
        print(self.firstname, self.lastname, 'teaches', self.course)

student = Student('Jane', 'Hirshfield', 'A+')
teacher = Teacher('Emily', 'Dickinson', 'poetry')

student.info()
teacher.info()

Output

Jane Hirshfield has a grade of A+
Emily Dickinson teaches poetry

Notes

It is common practice to put the super-class initialization as the first statement in the sub-class' __init__ function.

One can also use the super() function instead of explicitly declaring the class name. When using super(), the self parameter is also removed.

Example

class Student(Person):
    def __init__(self, fname, lname, grade):
        super().__init__(fname, lname)
        self.grade = grade

    def info(self):
         print(self.firstname, self.lastname, 'has a grade of', self.grade)

class Teacher(Person):
    def __init__(self, fname, lname, course):
        super().__init__(fname, lname)
        self.course = course

Lastly, the hierarchy of the class structure is not limited to just a class and its super-class. A class can be derived from a super-class, which in turn is derived from a super-super-class, etc.