Python Comments and Indentation

"Code is read much more often than it is written." - Guido van Rossum (Creator of Python)

To write professional Python, you must master two critical tools: Comments (which explain logic) and Indentation (which defines structure).

Python Comments

A comment is a text note written directly in your code that the computer ignores. It allows you to document your logic without affecting the program execution.

1. Single-Line Comments

A single-line comment is a note that occupies only one line of text. It is used to explain the code immediately following it.

Syntax: Type the hash symbol (#). Python ignores everything after this symbol on that specific line.

# This is a single-line comment
print("Hello World")

2. Inline Comments

An inline comment is a short note placed on the exact same line as a code statement.

Syntax: Type the code statement, add at least two spaces, then type the hash symbol (#) followed by your note.

x = 5  # This is an inline comment

Exercise 1: Annotating Logic

The code below calculates a price, but the context is missing. Add two comments:

1. A Single-Line Comment above the math explaining the business rule ("Apply Holiday Discount").
2. An Inline Comment next to the variable explaining the value ("15% rate").

# Apply Holiday Discount
rate = 0.15  # 15% rate
price = 200
final_price = price - (price * rate)
print(final_price)

Your output will appear here...

3. Docstrings (Documentation Strings)

A Docstring is a multi-line string used to document a specific segment of code, such as a function or a class. Unlike standard comments, Docstrings are retained by Python at runtime.

Syntax: Enclose the text in triple quotes ("""). This must be the very first line inside the function.

Exercise 2: Writing a Docstring

The function below has no documentation. Wrap the description text in triple quotes to create a valid Docstring.

def calculate_area(radius):
    """
    Calculates the area of a circle.
    Takes radius as an argument.
    Returns the area value.
    """
    pi = 3.14
    return pi * (radius ** 2)

print(calculate_area(5))

Your output will appear here...

Indentation and Structure

In many programming languages, curly braces {} are used to group code. Python uses Indentation.

1. Indentation

Indentation is the empty whitespace at the beginning of a line of code.

It tells Python which lines of code belong to a specific block.

Syntax Rule: Use 4 spaces per indentation level.

2. Blocks and Scope

A "Block" is a group of statements that execute together. "Scope" refers to the context in which that block is valid.

Syntax Rule: Any statement ending in a colon (:) starts a new block. All subsequent lines indented by 4 spaces belong to that block.

Exercise 3: Defining a Block

The Logic: The "Access Granted" message should only print if the password is correct. It must be inside the if block.

Task: Indent the print statement by 4 spaces to move it inside the block.

password = "wrong_password"

if password == "secret_code":
    # Inside the block (Indented)
    print("Access Granted!")

# Outside the block (Un-indented)
print("Login attempt finished.")

Your output will appear here...

3. Nested Blocks

Nesting is the practice of placing one code block inside another code block (e.g., an if statement inside a for loop).

Syntax Rule: Increase indentation by 4 spaces for every new block depth.

• Level 0 (0 spaces): Main program.
• Level 1 (4 spaces): Inside the first block.
• Level 2 (8 spaces): Inside the second (nested) block.

Exercise 4: Structure Nested Logic

We need to filter a list of temperatures. Organize the code structure using correct indentation:

1. The if statement must be inside the Loop (Level 1).
2. The print statement must be inside the If check (Level 2).

temps = [102, 98, 105, 99]

for t in temps:
    # Level 1: Inside the loop
    if t > 100:
        # Level 2: Inside the If
        print(f"Warning: {t} is too high!")

Your output will appear here...

Best Practices Checklist

Before writing production code, verify your style against these standards.

Final Challenge: Refactoring Code

The code below is unreadable and lacks documentation.

Your Mission:

1. Add a Docstring explaining the function's purpose.
2. Indent the logic correctly inside the function and loop.
3. Add one comment explaining the business logic of the if check.

def process_numbers(data):
    """
    Calculates the sum of all positive numbers in a list.
    """
    total = 0
    for num in data:
        # Business Logic: Only include positive numbers
        if num > 0:
            total += num
    return total

result = process_numbers([10, -5, 20, -1])
print(f"Sum of positives: {result}")

Your output will appear here...