Table of Contents
Introduction
Welcome back to another exciting tutorial on “Object oriented Programming OOPs in Python”. In this Python tutorial, you’ll learn about the class,instance,constructor of the class etc .
You will learn :-
- Overview Of Object Oriented Programming
- How to create class in python
- Instance of the class
- Constructors of python class
If you aren’t following along, I would recommend you to go back where you left or start from here.
An Overview of OOPs in Python
There are different ways to write a program to conquer a problem . Also , there are different paradigm under which we classify programming languages . One way is object oriented programming(OOPs).
To study more about programming paradigms , click here.
Class
A class is a template or structure or prototype written by the programmer for creation of objects.
A class contain sets of attributes (features of the class) and methods( functions that manipulate attributes or use them to achieve some output ) that are common to all the objects of this class.
Example : –
Consider a circle class , a class that represent the structure or template of the circles . A circle consists of features like radius ,diameter ( 2*radius). Consider an extra feature say color.
Under methods , we can define Perimeter (2*pi*r) and Area (pi*r*r) of the circle class.
Instance (Or Object)
An object is the instance of the class . Every object of the class holds different memory position in the program .
Example :- Consider the example of circle class, we define two objects C1 and C2 for class circle . One with color attribute set to aqua blue and other with color yellow .
The radius attribute is set to 190 mm and 125 mm respectively.Similarly , we can create as many object as needed and find perimeter or area for each of them.
Creating a Class in Python
A class in python is created in same way as function in python with some tweaks.
class clause is used to create a class in python . Naming convention for class name is generally UpperCamelCase (first letter of every word should be capital).
SYNTAX
class MyClass:
doc string # optional
Statement 1
Statement 2
Statement 3
…………………..
…………………..
Statement N
The statement includes class variables, class methods , instance variables etc which we will be discussing in later section.
Empty Class and the need of the Constructor
Let us create an empty Student class.
>>> class Student: ... pass ... >>> >>> Student <class '__main__.Student'>
Now , we can create instances for this Student class .
>>> S1 = Student() >>> S2 = Student() >>> >>> print(S1) <__main__.Student object at 0x7fc3b3396b80> >>> print(S2) <__main__.Student object at 0x7fc3b1dfefd0> >>>
S1 and S2 are two different objects of same class .
We can initialized some instance variables for S1 and S2.
>>> S1.Name = "JOHN" >>> S1.Age = 17 >>> >>> S2.Name = "PETER" >>> S2.Age = 18 >>> >>> print(S1.Name) JOHN >>> print(S2.Name) PETER >>>
Similarly , we can create various student objects and initialized the value of name and age for them .
But as the number of student increases the above process of initializing variables will become a difficult task and more prone to errors.
To resolve this issue , the constructor came into play .
Constructor of theClass
A constructor is used to initialize the data members of the object when it is created.
SYNTAX
class Myclass:
def __init__(self,args*):
…………
body of constructor
………….
TYPES OF CONSTRUCTOR
1. Default Constructor
When we don’t declare __init__ function in the class , it become default constructor. The python implicitly took care of this scenario and create the class.
>>> class Student: ... name = 'Student' ... >>> S1 = Student() >>> print(S1.name) Student >>>
In the above example , there is no __init__ methods yet python interpreter doesn’t show any error because this is a valid way to declare a class.
2. Parameterized Constructor
It contains some more arguments other than self.
self is always the first argument.
>>> class Student:
... def __init__(self,name):
... self.name = name
...
>>> S1 = Student('John')
>>> print(S1.name) John
>>> S2 = Student('Peter')
>>> print(S2.name) Peter
>>>
In the above example , name is passed as an argument when object is created and the instance variable is initialized by the constructor.
3. Non - Parameterized Constructor
It doesn’t contain any argument other than self ( reference to the instance being created).
>>> class Student: ... def __init__(self): ... self.Name = "Student" ... >>> S1 = Student() >>> print(S1.Name) Student >>
4. Python Trick : What if we create more than one constructor for a class ?
Let us create three constructor for a class.
>>> class X:
... def __init__(self):
... print('I am Ist')
... def __init__(self):
... print('I am Second')
... def __init__(self):
... print('I am Third')
...
>>> x1 = X()
I am Third
>>>
Hence , the instance always called the last constructor during instantiation.
Python doesn’t has the concept of Constructor Overloading.
Conclusion
Now , you are familiar with some terminologies like class,instance, constructor etc . We can proceed further to understand members of the class . In the next tutorial, we are going to focus on the variables and methods of the class and their types .
Last but not the least, do leave your feedback and suggestions. We would love to hear your feedback.
Till then , keep coding.
