PythonPlaza.com

Class/Objects in Python

A Class is a blueprint or a template, and an object is an instance of a class. For example, a Car is a class, while different brands of cars like Toyota, Honda, and Lexus can be objects of the Car class. Once a class is created, several objects can be created from that class that can have access to all the methods of the class.

A Python class has to start with a class keyword followed by the name of the class and a colon. Every class has __init__ Method called as (Constructor): It is invoked automatically when a new instance of the class is created. In other words, when an object is created. A class can have several methods. Each method starts with the def keyword, followed by the method name, and always self is passed as the first parameter. It refers to the instance of the class on which the method is invoked. The self allows the method to access/modify the class attributes


Code Example 1:
#Python Class

class MyClass:

   def __init__(self, varName, varMessage):
    self.name=varName
    self.message=varMessage

   def printMessage(self):
    print(f"Message from {self.name} is : {self.message}")


  obj=MyClass("Mike","I like swimming")
  
#Print:
print(obj.printMessage())
  
#Output:
Message from Mike is : I like swimming

init() Method

All python classes have __init__() as a built-in method. It is always executed when the class is initiated. It is used to assign values to properties of the object, or perform operations that are necessary when an object is created from a class. It is called automatically whenever new object is created from a class.so, __init__() makes it easier to create objects and assign initial values to them.


Code Example 2:
#Python Class:
class Student:
  def __init__(self, name, age):
    self.student_name = name
    self.student_major = age

p1 = Student("David", "Civil Engineering")

#Print:
print(p1.student_name)
print(p1.student_major)

#Output:
David
Civil Engineering

Instance & Class Variables

Instance Variables in a Python class are defined and initialized inside the __init__ method. The Instance Variables are created by the following syntax inside the __init__ method.
self.name_of_the_variable = value_assigned
The object of the class can access it. Changing the value of an instance variable only impacts the specific object or the instance. A class variable is defined within the class and is not part of any method or function of the class. It can be accessed outside of the class using the class name. Changing the instance variable affects all the objects/instances of the class.


Code Example 3:
#Class to demonstrate Class & Instance variables.
class Employee:

  #company_name is a class variable
  company_name=""

  def __init__(self, name,department):
    self.name = name
    self.major = department


  def show_employee_details(self):
    print(f" Employee Name: {name}")
    print(f" Employee Department: {department}")



 #let's create the object.
 employeeA=Employee('Mike Miller','ABC Corporation')
 employeeA.show_employee_details()


#Output:
 Employee Name: Mike Miller
 Employee Department: ABC Corporation

Static Methods and Class Methods

In python classes, class method and static methods are very common. When you define a class Method, you have to pass cls as the first parameter. A static method does not need any specific parameter. You can access other class variables inside the class method and modify them. The static methods do not need self or cls as first parameter, they are basically utilify functions that can take some paremeters and return some values. Staic methods can access the class variables using the class name. Use @classmethod decorator create a class method and @staticmethod to create a static method.


Code Example 4:
#Static Methods & Class Methods.
class FavoriteFruit:
    class_variable = ""

    def __init__(self, person_name, fruit_name):
        self.name=person_name
        self.fruit= fruit_name

    #Instance method (takes 'self' as the first argument)
    def instance_method(self):
        print(f"Hi {self.name}! Your favorite fruit is: {self.fruit}")

    @classmethod
    def class_method(cls):
       print(f"{cls.class_variable}")

    @staticmethod
    def static_method():
        print("Thanks for selecting your favorite fruit")



favFruit=FavoriteFruit('Wilson', 'Carrots')
FavoriteFruit.class_variable='Your Favorite Fruit'
favFruit.class_method()
favFruit.instance_method()
favFruit.static_method()


#Output:
Your Favorite Fruit
Hi Wilson! Your favorite fruit is: Carrots
Thanks for selecting your favorite fruit

Introduction	Variables	If-else
Strings	Functions	while-loop
For-Loop	List	Set
Dictionary	Tuple	Try..Except
Class/Object	Inheritance	Polymorphism
File Handling

Python

Object-oriented programming

Class/Objects in Python

__init__() Method

Instance & Class Variables

Static Methods and Class Methods

init() Method