Comments in Python - Mini Project: Build & Apply

Comments in Python

📖 Scenario: You are writing a simple program to calculate the total cost of items you want to buy. To keep your code clear, you will add comments explaining each part.

🎯 Goal: Learn how to write comments in Python to explain your code clearly.

📋 What You'll Learn

Create a variable with a specific value

Add a comment explaining the variable

Write a simple calculation with a comment

Print the result with a comment

💡 Why This Matters

🌍 Real World

Comments are used by programmers to explain their code to others and to themselves when they come back later.

💼 Career

Writing clear comments is important in any programming job to help teams work together and maintain code easily.

1

Create a variable with a comment

Create a variable called price and set it to 100. Add a comment above it that says # Price of the item.

Python

# Price of the item
# Your code here

Hint

Use # to start a comment. Write the comment on the line before the variable.

2

Add a comment for a discount variable

Add a variable called discount and set it to 20. Add a comment above it that says # Discount amount.

Python

# Price of the item
price = 100
# Discount amount
# Your code here

Hint

Remember to add the comment on the line before the variable.

3

Calculate total with a comment

Create a variable called total that subtracts discount from price. Add a comment above it that says # Calculate total price after discount.

Python

# Price of the item
price = 100
# Discount amount
discount = 20
# Calculate total price after discount
# Your code here

Hint

Use the minus sign - to subtract discount from price.

4

Print the total with a comment

Add a comment that says # Print the total price and then print the variable total.

Python

# Price of the item
price = 100
# Discount amount
discount = 20
# Calculate total price after discount
total = price - discount
# Print the total price
# Your code here

Hint

Use print(total) to show the result.

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