I recently I had to work with a large legacy codebase. It was especially confusing as there was no documentation available. In order to get myself up to speed as quickly as possible, I invested some time in finding some tools to aid me in understanding the architecture of the codebase.

Here are some tools I found which might be useful to you:

1. gource

   A really cool visualisation library that lets you generate a movie of all the commits on a codebase in real-time. It’s not very scientific but I like that it gives you an overall sense of the history of a project. It visualises the the authors as well as the file types committed.

2. PySnooper

   A useful tool when working with a legacy codebase and you don’t have the ability to load the entire beast into an IDE. Allows you to tactically insert a single debug line and get feedback immediately.

3. py-spy

   This tool works with a running process. You point it to the process PID and it can generate flamegraps as well as real-time top visualition. It is especially useful if you do not have access to any source code and you’re trying to figure out what a process is doing.

4. Speedscope

   This is tool is an alternative to flamegraphs. It’s an interactive, web-based viewer for performance profiles. It allows to you to drill down into a process to see where its spending its CPU cycles, RAM or time. I used it to profile my Django tests to see if there was an opportunity to speed them up.