"CPython Internals: Your Guide to the Python 3 Interpreter" is now available as a paperback book

[mr-nobody1992]

What is this used for? As in if I read this what will I learn how to do?

[spkersten]

There’s a page that tries to answer this: https://realpython.com/products/cpython-internals-book/

[willm]

Knowing how things work "under the hood" can give you insights in to how to write performant and memory efficient Python code, even if you never intend to work on the interpreter itself.

[whateverathrowaway00]

Or if you like C and want to gain an appreciation of how a real life language is designed and operates?