Embedding/Extending Python in/with C++: non-static members?

dmoore damienlmoore at gmail.com
Mon Jul 16 15:45:33 CEST 2007


Hi Folks:

I have a question about the use of static members in Python/C
extensions. Take the simple example from the "Extending and Embedding
the Python Interpreter" docs:

A simple module method:

static PyObject *
spam_system(PyObject *self, PyObject *args)
{
 ...
}

listed in a method table:

static PyMethodDef SpamMethods[] = {
    ...
    {"system",  spam_system, METH_VARARGS,
     "Execute a shell command."},
    ...
    {NULL, NULL, 0, NULL}        /* Sentinel */
};

that is registered with:

PyMODINIT_FUNC
initspam(void)
{
    (void) Py_InitModule("spam", SpamMethods);
}

I have an application that embed multiple interpreters. I want to be
able to register methods for each interpreter that access C++ state
data relevant to that particular interpreter. In other words I want to
be able to register non-static class members in a class like the
following:

class PythonSpamModuleInstance
{
    PythonSpamModuleInstance()
    {
        SpamMethods[0]={"system",  spam_system, METH_VARARGS,"Execute
a shell command."};
        SpamMethods[1]={NULL, NULL, 0, NULL};
        PyObject *spammodule=Py_InitModule("spam", SpamMethods); //
Needs an INCREF call?
    }
    ~PythonSpamModuleInstance()
    {
        PyObject_Del("spam", SpamMethods);
    }
    PyObject *spam_system(PyObject *self, PyObject *args)
    {
         // accesses non-static data in this class
    }
    PyMethodDef SpamMethods[2];
    PyObject *spammodule;
    // Other data specific to this instance of the module
};

The idea is that each time my app launches an embedded Interpreter it
will create an accompanying instance of PythonSpamModuleInstance that
allows the Interpreter to call the registered non-static C++ member
function spam_system. Calls to that member function will also affect
state information.

So the questions: will this work? In particular, will the use of non-
static member functions cause problems? Is there a better way of
creating extension modules for multiple embedded interpreters? If I am
forced to use static methods, how do i figure out which interpreter is
calling them?




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