Re: [newbie] Question on embedding/extending with boost::python

Cross-posted to the C++ Sig. Please post all further replies there.

Chris Heald wrote:
> Hi all --
>
> I'm working on an app that is going to be a C++ code engine which will be
> heavily extended through a series of Python scripts (objects, really). My
> desired requirements are as follows:
[snip]
> having trouble is with c and d - how do I give a Python app hooks into an
> existing C++ state machine? I know I can write an extension easily enough,
> but by my understanding, that will simply give the Python object access to a
> series of functions, and not the objects contained in the state machine that
> the interpreter is running under. I could use "pull" operations, wherein the
> C++ app polls the objects for changed state in a loop and updates its sate
> accordingly, but that seems that it wouldn't perform nearly so well as if
> the Python scripts were able to update the C++ state machine themselves, so
> I'm avoiding that route.

I'm not entirely sure what your problem is.

Have you looked at libs/python/test/embedding.cpp? It shows how your 
embedded interpreter can get access to the internals of the running C++ 
program. (Specifically, its classes.) Perhaps you can use that as a 
starting point?

> I had a co-worker suggest that I use Python as my primary execution
> environment instead of C++. While this would admittedly make some things
> easier, how much performance would I sacrifice with this route? I'm building
> a 3D application, and it doesn't seem that Python would be well-suited to
> such an application in terms of performance. There is potential for
> literally tens of thousands of instances of these objects to exist in this
> state machine, and I certainly don't want to hinder performance by moving
> the primary execution into an interpreted environment rather than a compiled
> environment.

Well, my common sense tells me that you may very well be right. But the 
important point is that there's really no way to tell, except for trying 
it out. (Profiling is the key.) And surely, writing the whole thing in 
Python (except for the critical sections) takes less time then writing 
the whole thing in C++ with just some things written in Python?

Taking this road could very well lead to disappointing performance as 
you say. But then you'd still have gained experience from making the 
Python prototype, and its C++ bits can most-likely be recycled anyway.

I don't really feel qualified to advise you to do one thing or the 
other. Embedding is sometimes the right/efficient way to do things, but 
such situations are becoming more and more rare. I am guessing that 
yours is such a situation, but you could argue that making a decision on 
such a guess is premature opimization (and therefore evil ;)). Perhaps 
others here can provide additional insights.

Regards,
Dirk Gerrits