I originally looked into using rusty-cheddar too. The thing which stopped me was that it doesn't look like it's being actively worked on and the rusty-binder project doesn't look like it's ready.
That said, it wasn't overly difficult to use syn to parse a chunk of code, then walk the parse tree storing any relevant function and struct definitions so they can be rendered at a later stage.
What's rust-cpython like for making Python bindings? Is there much benefit with using that over something like cffi and loading the *.so manually?