Calling Python functions from C++

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?