Python Comments

What are Python Comments?

A comment in Python is a line (or part of a line) that:

✅ Is ignored by Python

✅ Does NOT run as code

✅ Is written for humans to read

Think of comments as notes inside your program that explain what is happening.

Simple Example

# This is a comment
print("Hello, world!")

Output:

Hello, world!

Python skips the comment and runs only the print() line.

Why Comments Are Important

Comments help you:

• Understand your own code later
• Make your code readable
• Explain complex logic
• Work with other developers
• Debug more easily

Without comments, code can become confusing very quickly.

Types of Python Comments

Python has two main types:

1️⃣ Single-Line Comment (#)

This is the most common.

# This is a single-line comment
print("Python is fun")

You can also place it after code:

print("Python")  # This prints a word

2️⃣ Multi-Line Comments (Using Triple Quotes)

Python does not have a true multi-line comment symbol like /* */.

Instead, we use:

"""
This is a multi-line comment
It can span many lines
"""

OR

'''
This is also a multi-line comment
'''

Technically these are multi-line strings, but they are used as comments when not assigned to a variable.

Python Comment Types

| Comment Type              | Symbol Used | Purpose                          | Example                          |
|---------------------------|------------|----------------------------------|----------------------------------|
| Single-line comment       | #          | Short explanation                | # This is a comment              |
| Inline comment            | #          | Comment after code               | print("Hi") # greeting           |
| Multi-line (doc/comment)  | """ """    | Long explanation or documentation| """ multi-line comment """       |
| Multi-line (doc/comment)  | ''' '''    | Same as above                    | ''' multi-line comment '''       |

Example

❌ Without Comments

x = 5
y = 10
z = x + y
print(z)

You may forget what this does later.

✅ With Comments

# First number
x = 5

# Second number
y = 10

# Add the two numbers
z = x + y

# Display the result
print(z)

Now everything is clear 👍

Using Comments to Disable Code (For Testing)

print("This will run")

# print("This will NOT run")

Where Comments Are Commonly Used

1. Explaining Variables

# Store the user's age
age = 25

2. Explaining Logic

# Check if the user is an adult
if age >= 18:
    print("Adult")

3. Creating Sections in Code

# =========================
# USER AUTHENTICATION
# =========================

Docstrings (Very Important in Python)

Docstrings are special multi-line comments used in:

• Functions
• Classes
• Modules

They explain what the code does.

Example

def add(a, b):
    """
    This function adds two numbers
    and returns the result.
    """
    return a + b

You can access it using:

print(add.__doc__)

Docstring vs Normal Comment

| Feature        | Normal Comment (#) | Docstring (""" """)        |
|---------------|--------------------|-----------------------------|
| Used for       | Small notes        | Documentation               |
| Accessible     | No                 | Yes                         |
| Used in        | Anywhere           | Functions, classes, modules |
| Multi-line     | No                 | Yes                         |

Beginner vs Good Comments

❌ Bad Comment

# add 1 to i
i = i + 1

This is obvious and unnecessary.

✅ Good Comment

# Increase login attempt count for security tracking
login_attempts += 1

Explains WHY, not just WHAT.

Best Practices

✔ Write comments for complex code

✔ Keep them short and clear

✔ Update comments when code changes

✔ Use docstrings for functions and classes

✔ Avoid obvious comments

Common Mistakes

1. Too Many Comments

# create variable
name = "Danny"

Not useful.

2. Outdated Comments

# stores email
username = "Danny"

This causes confusion.

3. Commenting Every Line

Makes code messy and harder to read.