Clean Code Principles: Write Code That Lasts

Why Clean Code Matters

You spend 10x more time reading code than writing it. Clean code saves teams thousands of hours in maintenance. It is not a luxury – it is professional responsibility.

Meaningful Names

# Bad
def calc(x, y, z):
    return x * y * (1 - z)

# Good
def calculate_discounted_price(price, quantity, discount_rate):
    return price * quantity * (1 - discount_rate)

# Bad
d = 86400

# Good
SECONDS_PER_DAY = 86400

Functions Should Do One Thing

# Bad - too many responsibilities
def process_user(data):
    validate(data)
    save_to_db(data)
    send_email(data)
    log_activity(data)

# Good - separated concerns
def validate_user(data):
    if not data.get("email"):
        raise ValueError("Email required")

def save_user(data):
    return db.users.insert(data)

def on_user_created(user):
    send_welcome_email(user.email)
    logger.info(f"User {user.email} created")

Comments: Explain Why, Not What

# Bad - restates the code
x = x + 1  # increment x

# Good - explains intent
# Retry counter starts at 1 because first attempt already failed
retry_count = 1

Avoid Magic Numbers

# Bad
if len(password) < 8:
    raise ValueError("Too short")

# Good
MIN_PASSWORD_LENGTH = 8
if len(password) < MIN_PASSWORD_LENGTH:
    raise ValueError(f"Must be at least {MIN_PASSWORD_LENGTH} chars")

The Boy Scout Rule

Leave the code better than you found it. Fix one small thing nearby when you are in a file. Over time, this keeps codebases healthy.

Refactoring Checklist

• Functions over 20 lines? Extract smaller functions
• Deeply nested conditions? Invert or extract
• Duplicate code? Create shared function
• Mysterious number? Make it a named constant
• Long parameter list? Group into an object