1) First make sure you can build your own Python and run it into a debugger.
So you can not only add print expressions but also break at points and follow the code flow.
If you have toolsl that let you trace function calls, perfect, you will need it.
2) Start with the file that implement the data types. They are very easy to understand and you improve your C language language skills while reading the code.
3) Make UML diagrams - simple drawing helper tools like Argo UML or MS Visio can help you here. Write down the code flow.
4) Read the startup code for python. See what and how the basic infrastructure is initialized.
6) Ty to understand the Python side 100% - even the harder implementation details, what an AST is and what bound and unbound methods are and how you would implement them. When you have a model in mind how you would write an python interpreter then you can go to the final master step.
7) Write a debugger extension with the provided fast debugger C API.
This helps you to improve your C skills.
8) Take the final master step and dive into the heart of the interpreter code. This is even hard to read and understand for a well skilled C programmer. Read how expressions are evaluation and method looksup are cached, frames are setup for scoping rules etc. It's difficult and complex - in terms of complexity and lines of code.
9) Start Adobe Photoshop and create a nice looking "Master of Python" diploma and put it on your office wall.
