Python Refactoring & Performance

Overview

Safe refactoring patterns, type safety enforcement, and performance optimization for Python/FastAPI backends.

Core principle: Never refactor without characterization tests. Never optimize without profiling. Always improve type coverage.

3-strikes rule: If the same refactoring approach fails 3 times, stop. The problem is architectural — escalate to system-design for a deeper review instead of thrashing.

Safe Refactoring Process

1. Write characterization tests — capture current behavior
2. Run mypy — baseline type errors
3. Refactor — change structure, preserve behavior
4. Verify — tests pass, mypy errors same or fewer
5. Clean up — remove temporary tests if redundant

Architecture Enforcement