Python Design Patterns

Design for the next real change, not for imagined future flexibility. Simpler code wins until complexity earns its keep.

For concrete before/after examples, read references/pattern-catalog.md.

Decision Principles

• KISS: choose the simplest design that satisfies current requirements.
• Single responsibility: one reason to change per function/class/module.
• Composition over inheritance: combine behavior explicitly before building fragile hierarchies.
• Rule of three: do not abstract two similar cases until a third proves the pattern is real.
• Dependency direction: business logic should not depend on framework glue.

Refactoring Workflow