Adding Comments to Your Code

As your Python scripts become more complex, perhaps involving several variables, calculations, or steps to process user input, keeping track of what each part does becomes increasingly important. Writing code that works is one thing; writing code that you and others can understand later is another skill entirely. This is where comments come in.

Comments are annotations within your code that Python ignores during execution. Their sole purpose is to explain the code to human readers. Think of them as notes you leave for yourself or collaborators to clarify the purpose, logic, or assumptions behind a piece of code.

Why Use Comments?

• Readability: Good comments make your code easier to understand at a glance. When you revisit your code after a break, or when someone else needs to work with it, comments provide context.
• Maintenance: When you need to fix bugs or add new features, understanding the existing code is the first step. Comments significantly speed up this process.
• Collaboration: If you're working on a team, comments are essential for communicating intent and logic to your colleagues.
• Explaining Complexity: Sometimes, the reason why code is written a certain way isn't immediately obvious. Comments can explain intricate logic, specific choices, or workarounds.

Writing Comments in Python

In Python, anything following a hash symbol (#) on a line is considered a comment and is disregarded by the interpreter.

# This is a full-line comment. It explains the general purpose of the code below.
principal = 1000  # This is an inline comment. It explains this specific variable.
rate = 0.05       # Annual interest rate
years = 3         # Investment duration in years

# Calculate simple interest
interest = principal * rate * years

# Print the result (we'll learn more about formatted printing later)
print("The calculated simple interest is:")
print(interest)

In this example:

• The first line is a comment explaining the overall goal.
• Comments after principal, rate, and years explain what each variable represents. Inline comments are useful for brief clarifications.
• The comment before the calculation explains the formula being used.
• The comment before print explains what the next lines will do.

What Makes a Good Comment?

While commenting is good, writing effective comments is even better. Here are some guidelines:

1. Explain the "Why," Not Just the "What": Avoid comments that merely restate what the code clearly does.

   • Less helpful: # Assign 5 to x
x = 5
   • More helpful: # Set the maximum number of retries
max_retries = 5

2. Keep Comments Up-to-Date: If you change the code, make sure you update the corresponding comments. Outdated comments can be more misleading than no comments at all.

3. Be Concise: Write clearly and avoid unnecessary jargon or overly long explanations. Get straight to the point.

4. Comment Complex Sections: If a piece of logic is tricky, involves multiple steps, or relies on a specific assumption, add comments to guide the reader.

5. Use Full Sentences (Often): While inline comments can be brief phrases, comments explaining larger blocks often benefit from being complete sentences.

Commenting Out Code

Comments are also frequently used to temporarily disable lines of code, often during debugging. If you suspect a line or block of code is causing a problem, you can "comment it out" by adding a # at the beginning of each line. This prevents Python from executing it without requiring you to delete the code entirely.

# --- Original code ---
# print("Starting calculation...")
# result = complex_calculation(data)
# print("Calculation complete.")

# --- Code with one line commented out for testing ---
print("Starting calculation...")
# result = complex_calculation(data) # Temporarily disable this line
print("Skipping calculation for now.")
# print("Calculation complete.")

Adding comments is a simple yet powerful practice. As you write more Python code, incorporating clear and concise comments will make your programs significantly easier to manage, debug, and share. Get into the habit of commenting your code as you write it; it's much easier than trying to remember your thought process weeks or months later.