Use cases for each method type in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a static method inside a class.

Python

class Calculator:
    @staticmethod
    def add(a, b):
        return a [1] b

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

The add method should return the sum of a and b, so the operator is +.

2fill in blank

medium

Complete the code to define a class method that returns the class name.

Python

class Person:
    @classmethod
    def get_class_name(cls):
        return cls.[1]

Drag options to blanks, or click blank then click option'

A__qualname__

Bname

C__class__

D__name__

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance attributes or incorrect class attributes.

The __qualname__ attribute of a class gives its qualified name, which is useful in class methods.

3fill in blank

hard

Fix the error in the instance method that returns the full name.

Python

class User:
    def __init__(self, first, last):
        self.first = first
        self.last = last
    def full_name([1]):
        return f"{self.first} {self.last}"

Drag options to blanks, or click blank then click option'

Auser

Bcls

Cthis

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using cls or other names instead of self.

Instance methods must have self as the first parameter to access instance attributes.

4fill in blank

hard

Fill both blanks to create a class method that creates an instance from a string.

Python

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author
    @classmethod
    def from_string(cls, book_str):
        title, author = book_str.split([1])
        return cls([2], author)

Drag options to blanks, or click blank then click option'

A", "

Btitle

Cauthor

D': '

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong split delimiter or passing wrong variable to constructor.

The string is split by a comma and space ", ". The first part is assigned to title which is passed to the constructor.

5fill in blank

hard

Fill all three blanks to create a static method that checks if a number is even.

Python

class NumberUtils:
    @staticmethod
    def is_even([1]):
        return [2] % [3] == 0

Drag options to blanks, or click blank then click option'

Anum

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter name or wrong divisor.

The static method takes a number num and returns True if it is divisible by 2 (even).

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