The clean architecture is the opposite of spaghetti code, where everything is interlaced and there are no single elements that can be easily detached from the rest and replaced without the whole system collapsing. The main point of the clean architecture is to make clear "what is where and why", and this should be your first concern while you design and implement a software system, whatever architecture or development methodology you want to follow.
This book is divided into two parts.
The first part is about Test-driven Development (TDD),
The second part introduces the clean architecture.
https://leanpub.com/clean-architectures-in-python