Comments

What are comments?

Comments are notes for humans that Python ignores. They’re like sticky notes in your code that explain what’s happening. Why write comments?

Help others understand your code
Help future you remember what you did
Disable code temporarily
Document complex logic

Single-line comments

Use # to start a comment:

# This is a comment
print("Hello")  # This is also a comment

# You can have multiple lines
# of comments by starting
# each line with a hash

age = 25  # Store user's age

Multi-line comments

For longer explanations, use triple quotes:

"""
This is a multi-line comment.
It can span several lines.
Great for longer explanations.
"""

def calculate_tip(bill):
    """
    Calculate 20% tip for a restaurant bill.
    Takes the bill amount and returns the tip.
    """
    return bill * 0.20

Technically, triple quotes create a string that Python doesn’t use. Real multi-line comments don’t exist in Python, but this works the same way!

When to use comments

Good comments explain WHY, not WHAT:

# Good: Explains why
# Using 1.0625 because sales tax in CA is 6.25%
total = subtotal * 1.0625

# Bad: States the obvious
# Multiply subtotal by 1.0625
total = subtotal * 1.0625

Best practices

Use descriptive variable names instead of comments when possible. days_in_week = 7 is clearer than d = 7 # days.

Temporary comments

Use comments to disable code temporarily:

print("Starting process...")
# print("Debug info")  # Uncomment for debugging
new_method()
# old_method()  # Keeping for reference

Common mistakes

Outdated comments

# Bad: Says 15% but does 20%
# Calculate 15% tip
tip = bill * 0.20

# Good: Accurate
# Calculate 20% tip (standard)
tip = bill * 0.20

Over-commenting obvious code

# Bad: Too obvious
x = 5  # Set x to 5
y = 10  # Set y to 10

# Good: Only explain complex parts
x = 5
y = 10
position = x + y  # Convert to linear index

What’s next?

Now that you know the basics and how to document your code, let’s test your understanding with practice exercises!

Practice & Exercises

Test and reinforce your understanding of Python basics

Getting started

Data types

Working with data

Control flow

Data structures

Packing & Unpacking

What are comments?

Single-line comments

Multi-line comments

When to use comments

Best practices

Temporary comments

Common mistakes

What’s next?

Practice & Exercises

​What are comments?

​Single-line comments

​Multi-line comments

​When to use comments

​Best practices

​Temporary comments

​Common mistakes

​What’s next?

Practice & Exercises

What are comments?

Single-line comments

Multi-line comments

When to use comments

Best practices

Temporary comments

Common mistakes

What’s next?