Python OOP Part 1

Python is an object-oriented programming language. Object-oriented programming (OOP) focuses on creating reusable patterns of code.

• Class — A blueprint created by a programmer for an object. This defines a set of attributes that will characterize any object that is instantiated from this class.
• Object — An instance of a class. This is the realized version of the class, where the class is manifested in the program.

We define classes by using the class keyword, similar to how we define functions by using the def keyword.

Objects can store data using ordinary variables that belong to the object. Variables that belong to an object or class are referred to as fields. Objects can also have functionality by using functions that belong to a class. Such functions are called methods of the class. This terminology is important because it helps us to differentiate between functions and variables which are independent and those which belong to a class or object. Collectively, the fields and methods can be referred to as the attributes of that class.

Fields are of two types - they can belong to each instance/object of the class or they can belong to the class itself. They are called instance variables and class variables respectively.

A class is created using the class keyword. The fields and methods of the class are listed in an indented block.

The self

Class methods have only one specific difference from ordinary functions - they must have an extra first name that has to be added to the beginning of the parameter list, but you do not give a value for this parameter when you call the method, Python will provide it. This particular variable refers to the object itself, and by convention, it is given the name self.

Although, you can give any name for this parameter, it is strongly recommended that you use the name self - any other name is definitely frowned upon. There are many advantages to using a standard name - any reader of your program will immediately recognize it and even specialized IDEs (Integrated Development Environments) can help you if you use self.

class Student:

    pass  # An empty block

s = Student ()

print(s)

We create a new class using the class statement and the name of the class. This is followed by an indented block of statements which form the body of the class. We create an object/instance of this class using the name of the class followed by a pair of parentheses.

class Student:

    def say_hi(self):

        print('Hello, how are you?')

s = Student ()

print(s)

The __init__ method

The __init__ method is run as soon as an object of a class is instantiated (i.e. created). The method is useful to do any initialization (i.e. passing initial values to your object) you want to do with your object. Notice the double underscores both at the beginning and at the end of the name.

Class and Instance Variables (Or attributes)

In Python, instance variables are variables whose value is assigned inside a constructor or method with self.

Class variables are variables whose value is assigned in class.

# Class for BCA Student

class BCAStudent:

          # Class Variable

          stream = 'bca'

          # The init method or constructor

          def __init__(self, roll):

         

                   # Instance Variable       

                   self.roll = roll      

# Objects of BCAStudent class

a = BCAStudent(101)

b = BCAStudent(102)

print(a.stream)

print(b.stream)

print(a.roll)

print(b.roll)

# Class variables can be accessed using class name also

print(BCAStudent.stream)

Output:

         bca

         bca

         101

         102

         bca