Use cases for each method type in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the use case of a static method

Which scenario best describes when to use a static method in a Python class?

A When the method needs to access or modify the class's attributes

B When the method performs a utility function that does not access instance or class data

C When the method is used to initialize a new instance of the class

D When the method needs to access or modify the instance's attributes

💡 Hint

Think about methods that don't need any information from the class or its objects.

A static method is used for utility functions that don't need to access instance or class data. It behaves like a regular function but lives inside the class for organization.

❓ Predict Output

intermediate

Output of a class method modifying class attribute

What is the output of this code?

Python

class Counter:
    count = 0

    @classmethod
    def increment(cls):
        cls.count += 1

Counter.increment()
Counter.increment()
print(Counter.count)

A 2

B 1

C 0

D Error

💡 Hint

Class methods can modify class-level data.

The class method increment increases the class attribute count by 1 each time it is called. After two calls, count becomes 2.

❓ Predict Output

intermediate

Output of instance method accessing instance data

What will this code print?

Python

class Person:
    def __init__(self, name):
        self.name = name

    def greet(self):
        return f"Hello, {self.name}!"

p = Person('Alice')
print(p.greet())

A Hello, !

B Hello, name!

C Hello, Alice!

D Error

💡 Hint

Instance methods use self to access data.

The instance method greet accesses the instance attribute name via self and returns a greeting with the actual name.

🧠 Conceptual

advanced

Choosing method type for factory pattern

Which method type is best suited to implement a factory method that creates instances of the class?

A Instance method

B Static method

C Property method

D Class method

💡 Hint

Factory methods often need to create instances and may need class information.

Class methods receive the class as the first argument and are commonly used as factory methods to create instances, possibly with different parameters or subclasses.

❓ Predict Output

expert

Output of mixed method calls in inheritance

What is the output of this code?

Python

class Base:
    @staticmethod
    def static_method():
        return 'Base static'

    @classmethod
    def class_method(cls):
        return f'{cls.__name__} class'

    def instance_method(self):
        return 'Base instance'

class Child(Base):
    @staticmethod
    def static_method():
        return 'Child static'

    @classmethod
    def class_method(cls):
        return f'{cls.__name__} class overridden'

    def instance_method(self):
        return 'Child instance'

c = Child()
print(c.static_method())
print(c.class_method())
print(c.instance_method())

A

Child static
Child class overridden
Child instance

B

Base static
Child class overridden
Base instance

C

Child static
Base class
Child instance

D

Base static
Base class
Base instance

💡 Hint

Look at which methods are overridden and how they are called.

The Child class overrides all three methods. Calling them on an instance of Child uses the overridden versions, so the output reflects the Child implementations.

Practice

1. Which method type in Python is used to access or modify data unique to each object instance?

easy

A. Global function

B. Instance method

C. Static method

D. Class method

Solution

1. Step 1: Understand instance methods

   Instance methods receive the object itself as the first argument and can access or modify instance-specific data.

2. Step 2: Compare with other methods

   Class methods work with class-level data, static methods don't access instance or class data, and global functions are outside the class.

3. Final Answer:

   Instance method -> Option B

4. Quick Check:

   Instance method = unique object data [OK]

Hint: Instance methods use 'self' to access object data [OK]

Common Mistakes:

• Confusing class methods with instance methods
• Thinking static methods access instance data
• Assuming global functions are methods

2. Which of the following is the correct way to define a class method in Python?

easy

A. def method():

B. def method(self):

C. @staticmethod\ndef method():

D. @classmethod\ndef method(cls):

Solution

1. Step 1: Recall class method syntax

   Class methods use the @classmethod decorator and receive the class as the first argument, usually named 'cls'.

2. Step 2: Check options

   @classmethod\ndef method(cls): matches this syntax exactly; others define instance or static methods or lack decorators.

3. Final Answer:

   @classmethod\ndef method(cls): -> Option D

4. Quick Check:

   Class method = @classmethod + cls parameter [OK]

Hint: Class methods use @classmethod and 'cls' parameter [OK]

Common Mistakes:

• Using 'self' instead of 'cls' for class methods
• Missing the @classmethod decorator
• Confusing static method syntax with class methods

3. What will be the output of this code?

class Example:
    count = 0

    def __init__(self):
        Example.count += 1

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

obj1 = Example()
obj2 = Example()
print(Example.get_count())

medium

A. 2

B. 0

C. 1

D. Error

Solution

1. Step 1: Understand the constructor behavior

   Each time an Example object is created, the class variable 'count' increases by 1. Two objects are created, so count becomes 2.

2. Step 2: Understand the class method output

   The class method 'get_count' returns the current value of 'count', which is 2 after creating two objects.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Class variable incremented twice = 2 [OK]

Hint: Class methods access shared data like 'count' [OK]

Common Mistakes:

• Thinking count resets per instance
• Confusing instance and class variables
• Expecting an error due to method call

4. Identify the error in this code snippet:

class Calculator:
    @staticmethod
    def add(x, y):
        return x + y

    @classmethod
    def multiply(cls, x, y):
        return x * y

print(Calculator.add(2, 3))
print(Calculator.multiply(2, 3))

medium

A. No error, code runs correctly

B. Class method 'multiply' missing 'self' parameter

C. Static method 'add' missing 'self' parameter

D. Class method 'multiply' missing 'cls' parameter

Solution

1. Step 1: Check static method definition

   Static methods do not require 'self' or 'cls'; 'add' is correctly defined with two parameters.

2. Step 2: Check class method definition

   Class method 'multiply' correctly has 'cls' as the first parameter and two others; usage is correct.

3. Final Answer:

   No error, code runs correctly -> Option A

4. Quick Check:

   Static and class methods correctly defined [OK]

Hint: Static methods no 'self'; class methods need 'cls' first [OK]

Common Mistakes:

• Expecting 'self' in static methods
• Confusing 'self' and 'cls' in class methods
• Assuming method calls require instance

5. You want to create a method in a class that logs a message but does not need access to instance or class data. Which method type should you use and why?

hard

A. Instance method, because it can access instance data

B. Class method, because it can access class data

C. Static method, because it does not require instance or class data

D. Global function, because it is outside the class

Solution

1. Step 1: Identify method requirements

   The method only logs a message and does not need to access instance or class data.

2. Step 2: Choose appropriate method type

   Static methods are designed for tasks related to the class but do not use instance or class data, making them ideal here.

3. Final Answer:

   Static method, because it does not require instance or class data -> Option C

4. Quick Check:

   Logging without data access = static method [OK]

Hint: Use static methods for utility tasks without data access [OK]

Common Mistakes:

• Using instance or class methods unnecessarily
• Confusing static methods with global functions
• Thinking logging requires instance data