Difference between method types in Python - Hands-On Comparison

Difference between method types

📖 Scenario: Imagine you are creating a simple program to manage a library. You want to understand how different types of methods work in a class to organize your code better.

🎯 Goal: You will create a class with instance, class, and static methods to see how each method type behaves and how to call them.

📋 What You'll Learn

Create a class called Library with an instance method, a class method, and a static method.

Use self for the instance method parameter.

Use cls for the class method parameter.

Call each method correctly and print their outputs.

💡 Why This Matters

🌍 Real World

Understanding method types helps organize code in programs like library systems, games, or business apps.

💼 Career

Knowing method types is essential for writing clean, maintainable code in software development jobs.

1

Create the Library class with an instance method

Create a class called Library. Inside it, write an instance method called instance_method that takes self and returns the string "This is an instance method."

Python

class Library:
    # Your code here

Hint

Remember, instance methods always have self as the first parameter.

2

Add a class method to Library

Add a class method called class_method to the Library class. It should take cls as a parameter and return the string "This is a class method." Use the @classmethod decorator.

Python

class Library:
    def instance_method(self):
        return "This is an instance method."

    # Your code here

Hint

Use @classmethod above the method and cls as the first parameter.

3

Add a static method to Library

Add a static method called static_method to the Library class. It should take no parameters and return the string "This is a static method." Use the @staticmethod decorator.

Python

class Library:
    def instance_method(self):
        return "This is an instance method."

    @classmethod
    def class_method(cls):
        return "This is a class method."

    # Your code here

Hint

Static methods do not take self or cls as parameters.

4

Call and print all three methods

Create an object called lib from the Library class. Then print the result of calling the instance method instance_method on lib, the class method class_method on Library, and the static method static_method on Library.

Python

class Library:
    def instance_method(self):
        return "This is an instance method."

    @classmethod
    def class_method(cls):
        return "This is a class method."

    @staticmethod
    def static_method():
        return "This is a static method."

# Your code here

Hint

Remember to create an object to call the instance method, but call class and static methods directly on the class.

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