Difference between method types in Python

Introduction

Methods are functions inside a class. Different types of methods help organize code and control how data is accessed or changed.

When you want a function that works with an object's data.

When you need a function related to the class but not to any one object.

When you want a function that can change or use class-level data.

Syntax

Python

class ClassName:
    def instance_method(self, args):
        # works with object data
        pass

    @classmethod
    def class_method(cls, args):
        # works with class data
        pass

    @staticmethod
    def static_method(args):
        # works without self or cls
        pass

instance_method always has self to access object data.

class_method uses cls to access class data and is marked with @classmethod.

Examples

Instance method: works with a specific dog object.

Python

class Dog:
    def bark(self):
        print('Woof!')

Class method: works with the class itself, not one dog.

Python

class Dog:
    species = 'Canine'

    @classmethod
    def get_species(cls):
        return cls.species

Static method: does not use object or class data.

Python

class Dog:
    @staticmethod
    def info():
        print('Dogs are friendly animals.')

Sample Program

This program shows three method types: instance method uses object data, class method uses class data, and static method works independently.

Python

class Car:
    wheels = 4  # class variable

    def __init__(self, color):
        self.color = color  # instance variable

    def show_color(self):
        print(f'This car is {self.color}.')  # instance method

    @classmethod
    def show_wheels(cls):
        print(f'A car has {cls.wheels} wheels.')  # class method

    @staticmethod
    def honk():
        print('Beep beep!')  # static method

my_car = Car('red')
my_car.show_color()
Car.show_wheels()
Car.honk()

Important Notes

Instance methods need an object to work.

Class methods can be called on the class or an object.

Static methods are like regular functions inside a class.

Summary

Instance methods use self to access object data.

Class methods use cls and @classmethod to access class data.

Static methods use @staticmethod and don't access object or class data.

Practice

1. Which method type in Python automatically receives the instance as the first argument named self?

easy

A. Instance method

B. Class method

C. Static method

D. Global function

Solution

1. Step 1: Understand method types

   Instance methods receive the instance as the first argument, usually named self.

2. Step 2: Identify method with self

   Class methods receive the class as cls, static methods receive no automatic first argument.

3. Final Answer:

   Instance method -> Option A

4. Quick Check:

   Method with self = Instance method [OK]

Hint: Look for self as first parameter for instance methods [OK]

Common Mistakes:

• Confusing cls with self
• Thinking static methods have self
• Mixing global functions with methods

2. Which decorator is used to define a class method in Python?

easy

A. @classmethod

B. @staticmethod

C. @instance

D. @class

Solution

1. Step 1: Recall Python decorators for methods

   Class methods use the @classmethod decorator to receive the class as the first argument.

2. Step 2: Identify correct decorator

   @staticmethod is for static methods, @instance and @class are invalid decorators.

3. Final Answer:

   @classmethod -> Option A

4. Quick Check:

   Class method decorator = @classmethod [OK]

Hint: Class methods always use @classmethod decorator [OK]

Common Mistakes:

• Using @staticmethod for class methods
• Assuming @instance is a valid decorator
• Confusing decorator names

3. What is the output of this code?

class MyClass:
    @staticmethod
    def greet():
        return 'Hello'

print(MyClass.greet())

medium

A. AttributeError

B. TypeError

C. None

D. 'Hello'

Solution

1. Step 1: Understand static method behavior

   Static methods do not require an instance or class argument and can be called directly on the class.

2. Step 2: Analyze the code output

   The static method greet returns the string 'Hello', so print(MyClass.greet()) outputs 'Hello'.

3. Final Answer:

   'Hello' -> Option D

4. Quick Check:

   Static method call returns 'Hello' [OK]

Hint: Static methods can be called on class without arguments [OK]

Common Mistakes:

• Expecting a TypeError for missing self
• Confusing static with instance method call
• Thinking static methods return None by default

4. Identify the error in this code:

class Example:
    @classmethod
    def show(cls):
        print(cls.value)

Example.show()

medium

A. Missing @staticmethod decorator

B. Method should use 'self' instead of 'cls'

C. Missing class attribute 'value'

D. Syntax error in method definition

Solution

1. Step 1: Check class method usage

   The method show is a class method and tries to print cls.value.

2. Step 2: Verify class attribute existence

   The class Example does not define value, so accessing cls.value causes an AttributeError at runtime.

3. Final Answer:

   Missing class attribute 'value' -> Option C

4. Quick Check:

   Class attribute missing causes error [OK]

Hint: Class methods need class attributes to access via cls [OK]

Common Mistakes:

• Confusing instance and class attributes
• Thinking @staticmethod fixes attribute errors
• Using 'self' in class methods incorrectly

5. You want a method that can be called on the class or instance but does NOT access instance or class data. Which method type should you use?

hard

A. Class method

B. Static method

C. Instance method

D. Property method

Solution

1. Step 1: Understand method access types

   Instance methods access instance data via self, class methods access class data via cls.

2. Step 2: Identify method without data access

   Static methods do not access instance or class data and can be called on both class and instance.

3. Final Answer:

   Static method -> Option B

4. Quick Check:

   No data access = Static method [OK]

Hint: No data access means use static method [OK]

Common Mistakes:

• Choosing instance or class method incorrectly
• Confusing property methods with static methods
• Assuming static methods access class data