methods.md

Python by Example: Methods

Methods are functions defined on a class. Instance methods take self and operate on the instance. Class methods take cls and use @classmethod—useful for alternate constructors. Static methods use @staticmethod and take neither—they're utility functions that logically belong to the class but don't need instance or class data.

What you'll learn:

• Instance methods vs class methods vs static methods
• When to use each
• Class attributes shared by all instances

class Counter:
    count = 0  # class attribute

    def __init__(self):
        Counter.count += 1
        self.id = Counter.count

    def instance_method(self):
        return f"I am instance {self.id}"

    @classmethod
    def get_count(cls):
        return cls.count

    @staticmethod
    def info():
        return "Counter tracks instance creation"


c1 = Counter()
c2 = Counter()
print(c1.instance_method())
print(Counter.get_count())
print(Counter.info())

Counter.count is shared—both instances increment it. get_count uses cls to access the class; info needs neither self nor cls. Use @staticmethod when the function is related to the class but doesn't use instance or class state.

To run this program:

$ python source/methods.py
I am instance 1
2
Counter tracks instance creation

Tip: Most methods are instance methods. Use @classmethod for factory methods; use @staticmethod sparingly for utilities.

Try it: Add a class method that creates a Counter and returns it with a specific id.

Source: methods.py

Next: Inheritance