Clean Code

Clean Code (Python)

"Always leave the campground cleaner than you found it." — Robert Baden-Powell

"Always check a module in cleaner than when you checked it out." — Robert C. Martin, Clean Code

Rule Chapters

Load the chapter that matches the work. Rule IDs (N1, C5, G25, F3, T9...) are defined in these files:

The Philosophy

You don't have to make every module perfect. You simply have to make it a little bit better than when you found it.

If we all followed this simple rule:

• Our systems would gradually get better as they evolved
• Teams would care for the system as a whole
• The relentless deterioration of software would end

When Working on Code

Every time you touch code, look for at least one small improvement:

Quick Wins (Do These Immediately)

• Rename a poorly named variable → references/names.md
• Delete a redundant comment → references/comments.md
• Remove dead code or unused imports
• Replace a magic number with a named constant
• Extract a deeply nested block into a well-named function

Deeper Improvements (When Time Allows)

• Split a function that does multiple things → references/functions.md
• Remove duplication (DRY) → references/general.md
• Add missing boundary checks
• Improve test coverage → references/tests.md

The Rule in Practice

# You're asked to fix a bug in this function:
def proc(d, x, flag=False):
    # process data
    for i in d:
        if i > 0:
            if flag:
                x.append(i * 1.0825)  # tax
            else:
                x.append(i)
    return x

# Don't just fix the bug and leave.
# Leave it cleaner:
TAX_RATE = 0.0825

def process_positive_values(
    values: list[float],
    apply_tax: bool = False
) -> list[float]:
    """Filter positive values, optionally applying tax."""
    rate = 1 + TAX_RATE if apply_tax else 1
    return [v * rate for v in values if v > 0]

What changed:

• ✅ Descriptive function name (N1)
• ✅ Clear parameter names (N1)
• ✅ Type hints (P3)
• ✅ Named constant for magic number (G25)
• ✅ No output argument mutation (F2)
• ✅ Useful docstring (C4)

The Mindset

Don't:

• Leave code worse than you found it
• Say "that's not my code"
• Wait for a dedicated refactoring sprint
• Make massive changes unrelated to your task

Do:

• Keep changes proportional to your task
• Improve the code you are already changing
• Leave a trail of quality improvements over time

AI Behavior

Apply cleanup only when the task IS cleanup (review, refactor, "clean this up" asks). When writing or fixing code, follow these rules for the NEW code you write; do not expand the diff with drive-by improvements to adjacent code the user didn't ask about.

When reviewing code:

1. Load references/full-catalog.md for comprehensive rule checking
2. Flag violations by rule number
3. Suggest incremental improvements, not complete rewrites

The Boy Scout Promise

Every piece of code you touch gets a little better. Not perfect—just better.

Over time, better compounds into excellent.