Creating a Class and Object in Python

1. Create Class

• Definition:
  • A class is a blueprint for creating objects.
  • It defines a set of attributes and methods that the created objects will have.

Example:

class MyClass:
    x = 5

• Explanation:
  • The keyword class is used to define a class.
  • MyClass is the name of the class.
  • x is a class attribute with a value of 5.

2. Create Object

• Definition:
  • An object is an instance of a class.
  • It can use the attributes and methods defined in the class.

Example:

p1 = MyClass()
print(p1.x)  # Output: 5

• Explanation:
  • p1 is an object of MyClass.
  • MyClass() creates an instance of the class.
  • p1.x accesses the attribute x of the class, which is 5.

Key Points

1. Class Definition:
   • A class is defined using the class keyword.
   • It contains attributes and methods that define the properties and behaviors of the objects created from the class.
2. Creating an Object:
   • An object is created by calling the class name followed by parentheses.
   • The object can access the attributes and methods defined in the class.
3. Attributes and Methods:
   • Attributes are variables that belong to the class.
   • Methods are functions defined inside the class that describe the behaviors of the objects.

Example with Methods

Example:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def greet(self):
        print(f"Hello, my name is {self.name} and I am {self.age} years old.")

p1 = Person("John", 36)
p1.greet()  # Output: Hello, my name is John and I am 36 years old.

• Explanation:
  • __init__ is a special method called a constructor that initializes the object’s attributes.
  • self refers to the instance of the class.
  • name and age are instance attributes.
  • greet is a method that prints a greeting message.

Summary

• Creating a Class: Use the class keyword to define a class with attributes and methods.
• Creating an Object: Instantiate the class to create an object that can use the class attributes and methods.
• Attributes and Methods: Define the properties and behaviors of the objects through attributes and methods.

if we create a = ‘abcd’

check the by print(type(a))

it will return class as string

Basic Class and Object

1. Creating a Class and an Object

class MyClass:
    x = 5

# Create an object
p1 = MyClass()
print(p1.x)
# Output: 5

Class with Methods

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def greet(self):
        print(f"Hello, my name is {self.name} and I am {self.age} years old.")

# Create an object
p1 = Person("John", 36)
p1.greet()
# Output: Hello, my name is John and I am 36 years old.

Advanced Examples

1. Class with Private Variables

class Person:
    def __init__(self, name, age):
        self.__name = name  # Private variable
        self.__age = age    # Private variable

    def greet(self):
        print(f"Hello, my name is {self.__name} and I am {self.__age} years old.")

# Create an object
p1 = Person("John", 36)
p1.greet()
# Output: Hello, my name is John and I am 36 years old.

Class Inheritance

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def greet(self):
        print(f"Hello, my name is {self.name} and I am {self.age} years old.")

class Student(Person):
    def __init__(self, name, age, student_id):
        super().__init__(name, age)
        self.student_id = student_id

    def display_id(self):
        print(f"My student ID is {self.student_id}")

# Create an object
s1 = Student("Alice", 20, "S12345")
s1.greet()
s1.display_id()
# Output:
# Hello, my name is Alice and I am 20 years old.
# My student ID is S12345

Class with Class Variables

class Employee:
    company_name = "ABC Corp"  # Class variable

    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def display_employee(self):
        print(f"Name: {self.name}, Salary: {self.salary}, Company: {Employee.company_name}")

# Create objects
e1 = Employee("John", 50000)
e2 = Employee("Alice", 60000)

e1.display_employee()
e2.display_employee()
# Output:
# Name: John, Salary: 50000, Company: ABC Corp
# Name: Alice, Salary: 60000, Company: ABC Corp

Class with Static Methods

class MathOperations:
    @staticmethod
    def add(a, b):
        return a + b

# Call static method without creating an object
result = MathOperations.add(5, 3)
print(result)
# Output: 8