C++ <-> Python: bidirectional communication

Question

I want to integrate a Python application into my C++ application. The communication has to be bidirectional, as shown in the following example:

C++:

void main() {
    # call python code

    return 0;
}

int computeResult(int value) {
    int result;
    // do stuff with value
    return result;
}

Python:

def run(value):
    result = computeResult(value)    # call computeResult of C++ code
    ...

for i in xrange(0, 10):
    run(i)

I thought about calling the Python code from C++ via embedded Python, but I don't know how I can call computeResult from my Python code. I don't want to create a new process everytime I call computeResult, so I would have to access the existing instance of my C++ application.

Any ideas would be appreciated, even if they don't use embedded Python.