Embedding Python into C++ application

Question

Context:

An ongoing problem we have been facing is unit testing our market data applications. These applications sit and observe data being retrieved from feeds and does something. Some critical events which are hard to trigger rarely occur and it is are difficult for the Testers to verify our applications perform correctly under all situations, hence we have to rely on unit tests.

These systems generally work by issuing callbacks (into our application) when an event has occurred, then our task to deal with this.

Solution I envision:

Is it possible to embed Python, or extend (not 100% clear on this), so that a tester could fire up a Python REPL and issue function calls that are akin to callbacks which are then handled by our C++ classes. Some form of dynamic manipulation of our objects at runtime.

Answer 1

I do something similar to this in one of my projects by using SWIG to generate python bindings for the relevant parts of the C++ code. Then I embed the interpreter as others have suggested. Having done that I can execute python code at will (e.g. PyRun_SimpleString), which can access C++ code. Normally I end up using something like a Singleton to make accessing specific C++ objects from python easier.

Also worth a mention is directors in swig python modules, which allow virtual functions to be handled much more intuitively. Depending on quite what you're doing you might find these very helpful.

Answer 2

What you want to do is possible, though not trivial to get right. It sounds like you want to embed (rather than extend) Python. Both topics are covered in the tutorial here.

There's quite a lot of work in mapping from C++ classes to Python classes, and there are a number of things that can go wrong in subtle ways, particularly with memory leaks and multithreading (if your existing code is multi-threaded). However, if it's only for use in a testing situation and stability is not mission-critical then it might be less of a problem.