OOP in Python | Set 3 (Inheritance, examples of object, issubclass and super)
Last Updated : 07 Jun, 2022
We have discussed following topics on Object Oriented Programming in Python
In this article, Inheritance is introduced. One of the major advantages of Object Oriented Programming is re-use. Inheritance is one of the mechanisms to achieve the same. In inheritance, a class (usually called superclass) is inherited by another class (usually called subclass). The subclass adds some attributes to superclass. Below is a sample Python program to show how inheritance is implemented in Python.
Python # A Python program to demonstrate inheritance # Base or Super class. Note object in bracket. # (Generally, object is made ancestor of all classes) # In Python 3.x "class Person" is # equivalent to "class Person(object)" class Person(object): # Constructor def __init__(self, name): self.name = name # To get name def getName(self): return self.name # To check if this person is employee def isEmployee(self): return False # Inherited or Sub class (Note Person in bracket) class Employee(Person): # Here we return true def isEmployee(self): return True # Driver code emp = Person("Geek1") # An Object of Person print(emp.getName(), emp.isEmployee()) emp = Employee("Geek2") # An Object of Employee print(emp.getName(), emp.isEmployee()) Output: ('Geek1', False) ('Geek2', True) How to check if a class is subclass of another? Python provides a function issubclass() that directly tells us if a class is subclass of another class.
Python # Python example to check if a class is # subclass of another class Base(object): pass # Empty Class class Derived(Base): pass # Empty Class # Driver Code print(issubclass(Derived, Base)) print(issubclass(Base, Derived)) d = Derived() b = Base() # b is not an instance of Derived print(isinstance(b, Derived)) # But d is an instance of Base print(isinstance(d, Base))
Output: True False False True
What is object class? Like Java Object class, in Python (from version 3.x), object is root of all classes. In Python 3.x, "class Test(object)" and "class Test" are same. In Python 2.x, "class Test(object)" creates a class with object as parent (called new style class) and "class Test" creates old style class (without object parent). Refer
this for more details.
Does Python support Multiple Inheritance? Unlike Java and like C++, Python supports multiple inheritance. We specify all parent classes as comma separated list in bracket.
Python # Python example to show working of multiple # inheritance class Base1(object): def __init__(self): self.str1 = "Geek1" print "Base1" class Base2(object): def __init__(self): self.str2 = "Geek2" print "Base2" class Derived(Base1, Base2): def __init__(self): # Calling constructors of Base1 # and Base2 classes Base1.__init__(self) Base2.__init__(self) print "Derived" def printStrs(self): print(self.str1, self.str2) ob = Derived() ob.printStrs()
Output: Base1 Base2 Derived ('Geek1', 'Geek2') How to access parent members in a subclass? - Using Parent class name Python
# Python example to show that base # class members can be accessed in # derived class using base class name class Base(object): # Constructor def __init__(self, x): self.x = x class Derived(Base): # Constructor def __init__(self, x, y): Base.x = x self.y = y def printXY(self): # print(self.x, self.y) will also work print(Base.x, self.y) # Driver Code d = Derived(10, 20) d.printXY()
- Using super() We can also access parent class members using super. Python
# Python example to show that base # class members can be accessed in # derived class using super() class Base(object): # Constructor def __init__(self, x): self.x = x class Derived(Base): # Constructor def __init__(self, x, y): ''' In Python 3.x, "super().__init__(name)" also works''' super(Derived, self).__init__(x) self.y = y def printXY(self): # Note that Base.x won't work here # because super() is used in constructor print(self.x, self.y) # Driver Code d = Derived(10, 20) d.printXY()
Note that the above two methods are not exactly the same. In the next article on inheritance, we will covering following topics. 1) How super works? How accessing a member through super and parent class name are different? 2) How Diamond problem is handled in Python? Exercise: Predict the output of following Python programs - Python
class X(object): def __init__(self, a): self.num = a def doubleup(self): self.num *= 2 class Y(X): def __init__(self, a): X.__init__(self, a) def tripleup(self): self.num *= 3 obj = Y(4) print(obj.num) obj.doubleup() print(obj.num) obj.tripleup() print(obj.num)
- Python
# Base or Super class class Person(object): def __init__(self, name): self.name = name def getName(self): return self.name def isEmployee(self): return False # Inherited or Subclass (Note Person in bracket) class Employee(Person): def __init__(self, name, eid): ''' In Python 3.0+, "super().__init__(name)" also works''' super(Employee, self).__init__(name) self.empID = eid def isEmployee(self): return True def getID(self): return self.empID # Driver code emp = Employee("Geek1", "E101") print(emp.getName(), emp.isEmployee(), emp.getID()) Output: ('Geek1', True, 'E101')