Python Syntax, Indentation & Comments

In most programming languages (C, C++, Java, JavaScript, Rust), code blocks are demarcated using curly braces { ... }, and indentation is purely cosmetic. In Python, whitespace indentation defines the logical block hierarchy of your program.

This design choice (known as the off-side rule) ensures that every Python codebase is visually uniform, readable, and eliminates entire classes of syntax bugs like dangling-else ambiguity.

The Indentation Rules:

1. A colon : signals the start of a new indented code block (after if, elif, else, for, while, def, class, try, with).
2. Every line within that block must be indented by exactly 4 spaces (the official PEP 8 standard).
3. When indentation returns to the outer indentation level, the block terminates automatically.

# Check voting eligibility based on age
age = 20

if age >= 18:
    # 4 spaces indentation marks the IF block:
    print("Eligible to vote! ✅")
    print("Please cast your vote responsibly.")
else:
    # 4 spaces indentation marks the ELSE block:
    print("Not eligible yet.")
    print("You must be 18 or older.")

# 0 spaces indentation: Executes unconditionally outside the if-else block
print("Verification check completed.")

Comments are explanatory annotations written by programmers to document code logic. The Python compiler completely strips comments during lexical analysis, resulting in zero memory or runtime performance cost.

In Python, single-line comments begin with the hash symbol (#). They can occupy their own line or follow a statement inline (separated by at least two spaces according to PEP 8):

# Step 1: Define pricing parameters
item_price = 45.00   # Price per unit in rupees
quantity = 3         # Number of items ordered
tax_rate = 0.05      # 5% GST tax rate

# Step 2: Calculate total amount including tax
subtotal = item_price * quantity
tax_amount = subtotal * tax_rate
final_total = subtotal + tax_amount

# Step 3: Display results
print("Subtotal: Rs.", subtotal)
print("Tax (5%): Rs.", tax_amount)
print("Final Total Bill: Rs.", round(final_total, 2))

According to the PEP 8 style guide, code lines should be limited to 79-99 characters for readability. The safest and most Pythonic way to wrap long expressions across multiple lines is by enclosing them in parentheses (), which activates implicit line continuation:

# Calculate total score across multiple academic subjects
# Parentheses () allow clean multi-line continuation without syntax errors:
total_score = (
    85     # Mathematics score
    + 92   # Physics score
    + 78   # Chemistry score
    - 5    # Late homework penalty
)

print("Final Calculated Total Score:", total_score)

A docstring (documentation string) is a string literal enclosed in triple quotes ("""...""") placed as the very first statement inside a function, class, or module.

Unlike regular # comments that disappear at compile time, docstrings are preserved in memory at runtime and can be inspected via the .__doc__ attribute or the built-in help() system:

def calculate_rectangle_area(length, width):
    """
    Calculate and return the area of a rectangle.
    
    Parameters:
        length (float): The length of the rectangle
        width (float): The width of the rectangle
        
    Returns:
        float: Calculated area (length * width)
    """
    return length * width

# Call function
area = calculate_rectangle_area(10, 5)
print("Calculated Area:", area)

# Inspect docstring at runtime
print("\n--- Function Docstring (.__doc__) ---")
print(calculate_rectangle_area.__doc__)