Getting C++ object from PyObject *

[Nikolai Kirsebom]

I'm using BOOST to integrate Python into our application.  Could
someone tell me how I get hold of the C++ object (pointer to the
object instance) from a PyObject *.

Example:
I have defined and exposed two C++ classes:

class MyObjectA
{
public:
  MyObject();
};

class MyObjectB
{
public:
  MyObjectB();
  void SetInput(PyObject *o);
};

In Python I'm able to write:

pa = MyObjectA()
pb = MyObjectB()

to create an instance of each of the classes.

Then using the exposed SetInput method of class MyObjectB:

pb.SetInput(pa)

How would I code the SetInput method:

void MyObjectB::SetInput(PyObject *o)
{
//Check that type of 'o' is an (instance) object of class 'MyObjectA'
//Fetch the pointer (reference) to the actual instance of MyObjectA
MyObjectA * ca = .....
}

Thanks for any help.

Nikolai