python-architecture

Structure CLI applications using command dispatcher pattern. Covers entry points, command routing, argument parsing, and explicit parameter flow. Use when building CLI tools or refactoring command structure.

Creates new Python service classes following Martin Fowler's Service Layer pattern with constructor-based dependency injection, proper layering (Core vs Composite), and static vs instance method conventions. Use when adding new services or refactoring business logic into service classes.

Determines the correct architectural layer (Entry Point/Service/Domain/Infrastructure) for code placement in Python applications using Service Layer pattern. Prevents layer violations and maintains separation of concerns. Use when adding new functionality, refactoring code, or unclear where code should live.

Writes unit tests for Python service classes using Arrange-Act-Assert pattern with proper mocking at boundaries. Tests behavior, not implementation. Mocks external systems only (API calls, file I/O, databases). Use when writing tests for services or fixing test coverage.

Follow Python code organization conventions including method ordering, datetime handling, circular import avoidance, and type annotations. Use when organizing service classes, handling dates, or structuring modules.

Apply constructor-based dependency injection with explicit configuration flow. Covers required dependencies, fail-fast principles, and avoiding optional parameters with default factories. Use when designing service constructors or managing dependencies.

Design domain models following parse-once principle with type-safe APIs, factory methods, and Repository pattern. Use when creating domain models, parsing data structures, or organizing business logic in models.