Calling Python functions from C++

Question

I am trying to achieve call Python functions from C++. I thought it could be achieved through function pointers, but it does not seem to be possible. I have been using boost.python to accomplish this.

Say there is a function defined in Python:

def callback(arg1, arg2):
    #do something
    return something

Now I need to pass this function to C++, so that it can be called from there. How do I write the code on C++ side using boost.python to achieve this?

Answer 1

If it might have any name:

Pass it to a function that takes a boost::python::object.

bp::object pycb; //global variable. could also store it in a map, etc
void register_callback(bp::object cb)
{
      pycb = cb;
}

If it is in a single known namespace with a consistent name:

bp::object pycb = bp::scope("namespace").attr("callback");

bp::object has operator() defined, so you call it just like any function

ret = pycb()

Answer 2

Not a clue. But you can use PyObject_Call() to call it once you have the function object.

Answer 3

I've not used it before, but the reference manual has a section called Calling Python Functions and Methods which seems to show how to do this.

Answer 4

I used PyRun_SimpleString("myFunction()") as quick hack, as my function's name was known, took no args and lived in the __main__ namespace. Note you additionally need to get lock GIL if you are multi-threaded.