Legacy to Clean: Refactoring Python for Maintainability

While previous chapters demonstrated Clean Architecture principles through greenfield development, real-world systems often present a different challenge. Existing applications, built under time pressure or before architectural best practices were established, frequently violate Clean Architecture’s fundamental principles. Their domain logic becomes tangled with frameworks, business rules mix with infrastructure concerns, and dependencies flow in all directions. Yet these systems often serve critical business needs and cannot simply be replaced.

Through our exploration of Clean Architecture transformation, we’ll discover how to systematically evolve legacy systems while maintaining their business value. We’ll see how Clean Architecture’s explicit boundaries and dependency rules provide clear guidance for improving existing systems, even under real-world constraints. You’ll learn how to identify...