Clean Python: Complete Reference

Enforces all Clean Code principles from Robert C. Martin's Chapter 17, adapted for Python.

Comments (C1-C5)

• C1: No metadata in comments (use Git)
• C2: Delete obsolete comments immediately
• C3: No redundant comments
• C4: Write comments well if you must
• C5: Never commit commented-out code

Environment (E1-E2)

• E1: One command to build (pip install -e ".[dev]")
• E2: One command to test (pytest)

Functions (F1-F4)

• F1: Maximum 3 arguments (use dataclasses for more)
• F2: No output arguments (return values)
• F3: No flag arguments (split functions)
• F4: Delete dead functions

General (G1-G36)

• G1: One language per file
• G2: Implement expected behavior
• G3: Handle boundary conditions
• G4: Don't override safeties
• G5: DRY - no duplication
• G6: Consistent abstraction levels
• G7: Base classes don't know children
• G8: Minimize public interface
• G9: Delete dead code
• G10: Variables near usage
• G11: Be consistent
• G12: Remove clutter
• G13: No artificial coupling
• G14: No feature envy
• G15: No selector arguments
• G16: No obscured intent
• G17: Code where expected
• G18: Prefer instance methods
• G19: Use explanatory variables
• G20: Function names say what they do
• G21: Understand the algorithm
• G22: Make dependencies physical
• G23: Prefer polymorphism to if/else
• G24: Follow conventions (PEP 8)
• G25: Named constants, not magic numbers
• G26: Be precise
• G27: Structure over convention
• G28: Encapsulate conditionals
• G29: Avoid negative conditionals
• G30: Functions do one thing
• G31: Make temporal coupling explicit
• G32: Don't be arbitrary
• G33: Encapsulate boundary conditions
• G34: One abstraction level per function
• G35: Config at high levels
• G36: Law of Demeter (no train wrecks)

Python-Specific (P1-P3)

These adapt the Java-specific rules (J1-J3) to Python conventions:

• P1: No wildcard imports (from x import *) — opposite of Java, per PEP 8
• P2: Use Enums, not magic constants — same principle as J3
• P3: Type hints on public interfaces — Python's equivalent of Java's static typing

Names (N1-N7)

• N1: Choose descriptive names
• N2: Right abstraction level
• N3: Use standard nomenclature
• N4: Unambiguous names
• N5: Name length matches scope
• N6: No encodings
• N7: Names describe side effects

Tests (T1-T9)

• T1: Test everything that could break
• T2: Use coverage tools
• T3: Don't skip trivial tests
• T4: Ignored test = ambiguity question
• T5: Test boundary conditions
• T6: Exhaustively test near bugs
• T7: Look for patterns in failures
• T8: Check coverage when debugging
• T9: Tests must be fast (< 100ms each)

Quick Reference Table

Category	Rule	One-Liner
Comments	C1	No metadata (use Git)
	C3	No redundant comments
	C5	No commented-out code
Functions	F1	Max 3 arguments
	F3	No flag arguments
	F4	Delete dead functions
General	G5	DRY—no duplication
	G9	Delete dead code
	G16	No obscured intent
	G23	Polymorphism over if/else
	G25	Named constants, not magic numbers
	G30	Functions do one thing
	G36	Law of Demeter (one dot)
Names	N1	Descriptive names
	N5	Name length matches scope
Tests	T5	Test boundary conditions
	T9	Tests must be fast

Anti-Patterns (Don't → Do)

❌ Don't	✅ Do
Comment every line	Delete obvious comments
Helper for one-liner	Inline the code
from x import *	Explicit imports
Magic number 86400	SECONDS_PER_DAY = 86400
process(data, True)	process_verbose(data)
Deep nesting	Guard clauses, early returns
obj.a.b.c.value	obj.get_value()
100+ line function	Split by responsibility

AI Behavior

When reviewing code, identify violations by rule number (e.g., "G5 violation: duplicated logic"). When fixing or editing code, report what was fixed (e.g., "Fixed: extracted magic number to SECONDS_PER_DAY (G25)").