PyArg_ParseTuple question

[Mark Crispin]

In a C module, I want to pick up the arguments for a Python call like:
     module.call("string1",["string2a", "string2b", "string2c"], "string3")
and stash these into:
 	char *arg1;
 	char *arg2[];
 	char *arg3;
All arguments are required, and we can assume that the arg2 vector is 
terminated with a null pointer.

It doesn't look like PyArg_ParseTuple will do this easily; and that 
instead I have to use either the "O!" format with a PyList prototype, or 
use "O&" and write a converter.

If I use "O!", at what level does it check?  In particular, does it just 
check that the argument is a list, so I can get away with something like:

static PyObject *call(PyObject *self, PyObject *args)
{
     char *arg1, **arg2, *arg3;
     PyObject *arg2obj;
     PyObject *list = PyList_New(0);
     PyObject *ret = NULL;
     if(PyArg_ParseTuple(args, "sO!s", &arg1, list, &arg2obj, &arg3) {
 	// grovel over arg2obj to get the number of members and make
 	//  sure they are all strings
 	// allocate a big enough arg2
 	// copy the string pointers.
         ret = doMyThing(arg1, arg2, arg3);
     }
     PyObject_del(list);
     return ret;
}

By the way,...

Python has tossed me a couple of curve balls, but all in all it's been 
quite reasonable.  I still haven't read though the Python tutorial (I 
really do need to get up to speed on all the data types), but I've been 
able to get a tremendous amount of work done in a very short period of 
time.

Oh, I've made it SEGV a few times, but these were all blunders in my C 
module, such as a C method returning self to indicate success (oops!).

Python is the best development environment since LISP and SmallTalk nearly 
20 years ago.  Coming from me, that's quite high praise.

-- Mark --

http://panda.com/mrc
Democracy is two wolves and a sheep deciding what to eat for lunch.
Liberty is a well-armed sheep contesting the vote.