Question

Given a PyObject* pointing to a python object, how do I invoke one of the object methods? The documentation never gives an example of this:

PyObject* obj = ....
PyObject* args = Py_BuildValue("(s)", "An arg");
PyObject* method = PyWHATGOESHERE(obj, "foo");
PyObject* ret = PyWHATGOESHERE(obj, method, args);
if (!ret) {
   // check error...
}

This would be the equivalent of

>>> ret = obj.foo("An arg")

Answer 1

PyObject* obj = ....
PyObject *ret = PyObject_CallMethod(obj, "foo", "(s)", "An arg");
if (!ret) {
   // check error...
}

Read up on the Python C API documentation. In this case, you want the object protocol.

PyObject* PyObject_CallMethod(PyObject *o, char *method, char *format, ...)

Return value: New reference.

Call the method named method of object o with a variable number of C
arguments. The C arguments are
described by a Py_BuildValue() format
string that should produce a tuple.
The format may be NULL, indicating
that no arguments are provided.
Returns the result of the call on
success, or NULL on failure. This is
the equivalent of the Python
expression o.method(args). Note that
if you only pass PyObject * args,
PyObject_CallMethodObjArgs() is a
faster alternative.

And

PyObject* PyObject_CallMethodObjArgs(PyObject *o, PyObject *name, ..., NULL)

Return value: New reference.

Calls a method of the object o, where the name of the method is given
as a Python string object in name. It
is called with a variable number of
PyObject* arguments. The arguments are
provided as a variable number of
parameters followed by NULL. Returns
the result of the call on success, or
NULL on failure.