Fix Python Bug

Simple bug-finding task for a Python programmer:

Task: Find the Bug in the Code Here is a short Python function that is supposed to return the square of a number, but it contains a bug. Your job is to find and fix the bug.

def square_number(num):
    result = num * num
    return result + 1

print(square_number(5))  # Expected output: 25

What’s wrong with this code? How can you fix it?

Original code:

def square_number(num):
    result = num * num
    return result + 1

print(square_number(5))  # Expected output: 25

What’s wrong? The function is supposed to return the square of the number num. Squaring means multiplying the number by itself, which is done correctly here by num * num. However, after computing the square, the function adds 1 to the result (return result + 1).

Explanation:

So when you call square_number(5):

It calculates 5 * 5 = 25

Then adds 1, giving 26

But the expected output is 25

How to fix it? Simply remove the + 1 part from the return statement so the function returns the correct squared value:

def square_number(num):
    result = num * num
    return result

print(square_number(5))  # Output: 25

Here are a few more simple bug-finding practice tasks for you:

Task 1: Find the Bug in the Average Function

The following function is intended to calculate the average of two numbers, but it contains a bug.

def average(a, b):
    return a + b / 2

print(average(4, 6))  # Expected output: 5

Find and fix the bug.

Task 2: List Index Error

This function tries to access the last item in a list, but there’s a bug.

def get_last_element(lst):
    return lst[len(lst)]

print(get_last_element([1, 2, 3]))  # Expected output: 3

Find and fix the bug.

Task 3: String Concatenation Issue Fix the bug so the function returns “Hello, World!”

def greet(name):
    return "Hello, " + name + "!"

print(greet(Hello, World))
def get_last_element(lst):
    return lst[len(lst)]

print(get_last_element([1, 2, 3]))  # Expected output: 3

Find and fix the bug.

Task 3: String Concatenation Issue

Fix the bug so the function returns “Hello, World!”

def greet(name):
    return "Hello, " + name + "!"

print(greet("World"))

def greet(name):
    return "Hello, " + name + "!"

print(greet(Hello, World))

Find and fix the bug.

Let’s go through the solutions for the three practice tasks I gave you:

Task 1: Find the Bug in the Average Function

Original code:

def average(a, b):
    return a + b / 2

print(average(4, 6))  # Expected output: 5

What’s wrong?

The function attempts to calculate the average of two numbers by computing a + b / 2. Due to operator precedence, this computes:

b / 2 first

then adds a

So for average(4, 6) it performs: 4 + (6 / 2) = 4 + 3 = 7

The expected output is 5 (since (4 + 6) / 2 = 5), so the calculation is incorrect.

How to fix it?

You need to add parentheses to ensure a + b is summed first, then divided by 2:

def average(a, b):
    return (a + b) / 2

print(average(4, 6))  # Output: 5

Task 2: List Index Error

Original code:

def get_last_element(lst):
    return lst[len(lst)]

print(get_last_element([1, 2, 3]))  # Expected output: 3

What’s wrong? List indices in Python are zero-based. len(lst) returns the length of the list, but valid indices range from 0 to len(lst) - 1.

For [1,len(lst) is 3, but valid indices are 0, 1, 2.

lst[len(lst)] tries to access lst, which raises an IndexError.

How to fix it? Use index len(lst) - 1 to get the last element:

def get_last_element(lst):
    return lst[len(lst) - 1]

print(get_last_element([1, 2, 3]))  # Output: 3

Alternatively, you can use negative indexing:

def get_last_element(lst):
    return lst[-1]

print(get_last_element([1, 2, 3]))  # Output: 3

Task 3: String Concatenation Issue

Original code:

def greet(name):
    return "Hello, " + name + "!"

def get_last_element(lst):
    return lst[-1]

print(get_last_element([1, 2, 3]))  # Output: 3

Task 3: String Concatenation Issue

Original code:

def greet(name):
    return "Hello, " + name + "!"

print(greet(Hello, World))

What’s wrong? In the print statement, greet(Hello, World) treats Hello and World as variables or identifiers instead of a single string argument. This will raise a NameError unless these variables are defined earlier.

Additionally, the function expects one argument (name), but two are given due to the comma.

How to fix it? Pass the argument as a single string (in quotes):

def greet(name):
    return "Hello, " + name + "!"

print(greet("World"))  # Output: Hello, World!

or if you want to greet “Hello, World!” specifically:

def greet(name):
    return "Hello, " + name + "!"

print(greet("Hello, World!"))

print(greet("World"))

Feel free to leave feedback I will always appreciate it!

• Python
• Bug Fix