Comments in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of code with inline comments

What is the output of this Python code with inline comments?

Python

x = 5  # assign 5 to x
# next line multiplies x by 2
y = x * 2
print(y)  # print the value of y

A 5

B 10

C SyntaxError

D null

💡 Hint

Look at the calculation done on x before printing y.

The comment lines do not affect the code execution. x is 5, y is x*2 which is 10, so print(y) outputs 10.

❓ Predict Output

intermediate

Effect of comments on code execution

What will be printed by this code?

Python

a = 3
# a = 10
print(a)

A SyntaxError

B 10

C 3

D null

💡 Hint

Check which line is commented out.

The line 'a = 10' is commented out, so it does not run. a remains 3, so print(a) outputs 3.

❓ Predict Output

advanced

Output with multi-line string used as comment

What is the output of this code?

Python

'''
This is a multi-line string
used as a comment
'''
print('Hello')

A SyntaxError

B

This is a multi-line string
used as a comment
Hello

C null

D Hello

💡 Hint

Multi-line strings not assigned to a variable are ignored by Python.

The triple quotes create a multi-line string that is not assigned or used, so it acts like a comment. Only 'Hello' is printed.

❓ Predict Output

advanced

Effect of comments inside code block

What will this code print?

Python

for i in range(3):
    # print(i)
    print(i + 1)

A

1
2
3

B

0
1
2

C SyntaxError

D null

💡 Hint

Look at which print statement is active inside the loop.

The first print is commented out, so only print(i + 1) runs, printing 1, 2, 3 on separate lines.

🧠 Conceptual

expert

Identifying error caused by misplaced comment

Which option will cause a SyntaxError due to incorrect comment placement?

A print(#'Hello')

B #print('Hello')

C print('Hello') # This is a comment

D print('Hello')

💡 Hint

Comments cannot start inside a string or expression.

Option A tries to start a comment inside the parentheses before the string ends, causing a SyntaxError.

Practice

1. What symbol is used to write a single-line comment in Python?

easy

A. /* */

B. //

C. #

D.

Solution

1. Step 1: Identify the comment symbol in Python

   Python uses the # symbol to start a single-line comment.

2. Step 2: Compare with other languages

   Other symbols like // or /* */ are used in languages like JavaScript or C, not Python.

3. Final Answer:

   # -> Option C

4. Quick Check:

   Single-line comment = # [OK]

Hint: Single-line comments start with # in Python [OK]

Common Mistakes:

• Using // instead of #
• Using /* */ for single-line comments
• Confusing HTML comments with Python

2. Which of the following is the correct way to write a multi-line comment in Python?

easy

A.

B. '''This is a multi-line comment'''

C. // This is a multi-line comment //

D. /* This is a multi-line comment */

Solution

1. Step 1: Recognize Python multi-line comment style

   Python uses triple single quotes ''' or triple double quotes """ for multi-line comments or docstrings.

2. Step 2: Eliminate other language comment styles

   Options A, B, and D are comment styles from other languages like HTML, JavaScript/C++, and C.

3. Final Answer:

   '''This is a multi-line comment''' -> Option B

4. Quick Check:

   Multi-line comment = triple quotes [OK]

Hint: Use triple quotes ''' or """ for multi-line comments [OK]

Common Mistakes:

• Using // or /* */ which are not Python syntax
• Using HTML style comments
• Trying to use # for multi-line comments without repeating

3. What will be the output of the following code?

print('Hello')  # This prints Hello
# print('World')

medium

A. Hello

B. SyntaxError

C. World

D. Hello\nWorld

Solution

1. Step 1: Understand the effect of comments on code execution

   The first line prints 'Hello' because the comment after it does not affect the print statement.

2. Step 2: Recognize that the second print is commented out

   The second print statement is fully commented out, so it does not run or print anything.

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   Commented code does not run = Hello [OK]

Hint: Code after # is ignored; only uncommented lines run [OK]

Common Mistakes:

• Thinking commented print runs
• Expecting both Hello and World printed
• Confusing comment with string

4. Find the error in this code snippet:

# This is a comment
print('Start')
'''This is a comment without an end
print('End')

medium

A. Comments cannot be placed before print statements

B. No error, code runs fine

C. print('End') is outside comment and runs normally

D. Missing closing triple quotes causes SyntaxError

Solution

1. Step 1: Check triple quote usage

   The triple quotes start a multi-line comment but are not closed, causing a syntax error.

2. Step 2: Understand impact on code parsing

   Without closing quotes, Python treats the rest as part of the string, leading to a SyntaxError.

3. Final Answer:

   Missing closing triple quotes causes SyntaxError -> Option D

4. Quick Check:

   Unclosed triple quotes = SyntaxError [OK]

Hint: Always close triple quotes to avoid syntax errors [OK]

Common Mistakes:

• Ignoring missing triple quote closure
• Thinking comments can be unclosed
• Assuming code after triple quotes runs

5. You want to temporarily disable a block of code without deleting it. Which is the best way to do this in Python?

hard

A. Put # at the start of each line in the block

B. Surround the code block with triple quotes ''' ... '''

C. Use /* ... */ around the block

D. Wrap the block in

Solution

1. Step 1: Understand Python comment styles for disabling code

   Python does not officially support block comments; the common way is to put # at the start of each line.

2. Step 2: Evaluate triple quotes usage

   Triple quotes create a string literal, which may not disable code properly and can cause unexpected behavior if used improperly.

3. Step 3: Recognize other language comment styles

   Options C and D are not valid in Python.

4. Final Answer:

   Put # at the start of each line in the block -> Option A

5. Quick Check:

   Disable code block = # per line [OK]

Hint: Use # on each line to disable code safely [OK]

Common Mistakes:

• Using triple quotes which may not disable code
• Using /* */ which is invalid in Python
• Using HTML comments which do nothing in Python