Question

I have a program written in C++ with a web interface to for the purpose of RPC. I can call http://localhost/ListVariables or http://localhost/RunFunction?var=1 and have the C code execute ListVariables or RunFunction. It works, but I’d rather not have to manage the web server in C/C++ when there are so many good Python web servers out there.

What I’m imagining is having the C program call into Python to start a web server on another thread (i.e. Tornado), return to C and then continue chugging along doing calculations. Then when the Python server receives a request on http://localhost/ListVariables, it calls back into C and executes ListVariables on the already running process.

C -----> processing -----------> processing ------------> RPC: FuncA -------->
 |                                                        ^        |
  \---> Python Web Server ---------- Request for: FuncA --/   ...   \-------->
                                     ^
  browser: http://localhost/FuncA ---/

The project has the unfortunate caveat that the program must be started from C to begin with. After doing some research this seems to be a bit of a border case, since Python–>C and C–>Python can be done with Cython. However, I can’t find many resources on C–>Python–>C, as most of the examples I’ve found describe linking to libraries and not to already-running processes. Is it possible to have Python call back into a running C program?

Answer 1

Absolutely. Create a “fake” module in the C program injected into sys.modules that the Python code can import and access as it would any other module.