All the fundamental behaviours (movement, combat, resource harvesting) are implemented in C.
The engine uses Python as a scripting/config language. You can use it to hook into a lot of events pushed from the engine core (unit got selected, unit started movement, unit started harvesting, etc.) and customize or change the unit behaviours.
My initial idea was that I wanted a more "sexy" language for scripting. Python is a lot more popular and (arguably) more enjoyable to use than Lua. There's a lot of cool stuff like list comprehensions. Plus I had a selfish reason of just wanting to learn more Python and fool around with the CPython code.
Over the duration of the project, I really did learn to appreciate why Lua is embedded into games and Python isn't. Lua is really small and you have full control over everything. And you're eventually going to need that control when you implement features like reflection, pausing the game, etc. CPython is this big shared library that does its' own thing and you have a lot less control over. The parts where it just doesn't expose enough through its' API do do what you want is a real huge pain. I ended up writing a bunch of code to serialize all the internal data structures and this was a massive chore. Also you have a lot less control over CPython's performance and memory allocations.
I didn't really appreciate these things when I started the project so hence I went with Python. But since I ended up doing it, I guess you can still enjoy the benefits of it.
