What is @classmethod, @staticmethod and regular instance methods in python?

In Python, @classmethod is a decorator used to define a method that is bound to the class and not the instance. It’s part of Python’s method types alongside @staticmethod and regular instance methods.

What is @classmethod?

• A @classmethod takes the class itself (cls) as its first argument, instead of self.

• It can access and modify class state that applies across all instances.

class Book:

    count = 0

    def __init__(self, title):

        self.title = title

        Book.count += 1

    @classmethod

    def get_count(cls):

        return cls.count

Book("A Tale of Two Cities")

Book("1984")

print(Book.get_count())  # Output: 2

Here, get_count() is a class method used to read a class-level variable, not tied to a single instance.

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🧠 When to Use @classmethod

• Factory methods (from_*) that return class instances:

class User:

    def __init__(self, name, age):

        self.name = name

        self.age = age

    @classmethod

    def from_string(cls, user_str):

        name, age = user_str.split(',')

        return cls(name, int(age))

user = User.from_string("Alice,30")

• Accessing or modifying class-level state

• Supporting inheritance-aware behavior

class MathUtils:

    @staticmethod

    def square(x):

        return x * x

print(MathUtils.square(4))  # Output: 16

Summary

• Use @classmethod when you need access to the class (cls)

• Use @staticmethod for utility functions that don’t need class or instance

• Use regular instance methods for behavior tied to an object

references:

OpenAI