Lesson 48: Class Methods

Class Methods and Static Methods

Python supports different types of methods: instance methods (regular methods), class methods, and static methods. Each serves a different purpose and is useful in different scenarios.

Understanding these method types helps you write more organized and efficient object-oriented code.

Instance Methods

Instance methods are the most common type. They take self as the first parameter and can access instance attributes:

instance_methods.py
class Circle:
    def __init__(self, radius):
        self.radius = radius
    
    # Instance method
    def area(self):
        return 3.14159 * self.radius ** 2
    
    def circumference(self):
        return 2 * 3.14159 * self.radius

circle = Circle(5)
print(circle.area())  # 78.54
print(circle.circumference())  # 31.42

Class Methods

Class methods take cls as the first parameter and can access class attributes. They're defined with @classmethod decorator:

class_methods.py
class Student:
    total_students = 0  # Class attribute
    
    def __init__(self, name):
        self.name = name
        Student.total_students += 1
    
    @classmethod
    def get_total(cls):
        return cls.total_students
    
    @classmethod
    def from_string(cls, student_str):
        # Alternative constructor
        name = student_str.split(",")[0]
        return cls(name)

student1 = Student("Alice")
student2 = Student("Bob")
print(Student.get_total())  # 2

student3 = Student.from_string("Charlie, 20")

Static Methods

Static methods don't take self or cls. They're defined with @staticmethod and are utility functions related to the class:

static_methods.py
class MathUtils:
    @staticmethod
    def add(a, b):
        return a + b
    
    @staticmethod
    def multiply(a, b):
        return a * b

# Can be called on class or instance
result1 = MathUtils.add(5, 3)  # 8
result2 = MathUtils.multiply(4, 2)  # 8

print(result1, result2)

Best Practices

✅ Method Type Guidelines

• Use instance methods for operations on specific objects

• Use class methods for operations on the class itself or alternative constructors

• Use static methods for utility functions related to the class

• Don't use static methods if you need access to instance or class data

Class Methods

Class Methods and Static Methods

Instance Methods

Class Methods

Static Methods

Best Practices

✅ Method Type Guidelines

Lesson Complete!