Creating Classes in Python

The class statement creates a new class definition. The name of the class immediately follows the keyword class followed by a colon as follows ?

class ClassName:
    'Optional class documentation string'
    class_suite

• The class has a documentation string, which can be accessed via ClassName.__doc__.
• The class_suite consists of all the component statements defining class members, data attributes and functions.

Basic Class Structure

A Python class contains attributes (data) and methods (functions). Here's the basic syntax ?

class Employee:
    'Common base class for all employees'
    empCount = 0  # Class variable
    
    def __init__(self, name, salary):
        self.name = name      # Instance variable
        self.salary = salary  # Instance variable
        Employee.empCount += 1
    
    def displayCount(self):
        print("Total Employee %d" % Employee.empCount)
    
    def displayEmployee(self):
        print("Name:", self.name, ", Salary:", self.salary)

# Creating instances
emp1 = Employee("John", 50000)
emp2 = Employee("Alice", 60000)

emp1.displayEmployee()
emp2.displayEmployee()
emp1.displayCount()

Name: John , Salary: 50000
Name: Alice , Salary: 60000
Total Employee 2

Key Components

Class Variables vs Instance Variables

class Student:
    school = "ABC School"  # Class variable (shared by all instances)
    
    def __init__(self, name, grade):
        self.name = name    # Instance variable (unique to each instance)
        self.grade = grade  # Instance variable

# Creating instances
student1 = Student("Bob", "A")
student2 = Student("Carol", "B")

print("School:", Student.school)  # Access class variable
print("Student 1:", student1.name, student1.grade)
print("Student 2:", student2.name, student2.grade)

School: ABC School
Student 1: Bob A
Student 2: Carol B

The __init__ Method

The __init__ method is a special method called the constructor. It initializes new instances of the class ?

class Car:
    def __init__(self, brand, model, year):
        self.brand = brand
        self.model = model
        self.year = year
    
    def display_info(self):
        return f"{self.year} {self.brand} {self.model}"

my_car = Car("Toyota", "Camry", 2023)
print(my_car.display_info())

2023 Toyota Camry

Class Methods and Self Parameter

Conclusion

Python classes use the class keyword to define blueprints for objects. The __init__ method initializes instances, while self refers to the current instance. Class variables are shared among all instances, while instance variables are unique to each object.