PyArg_ParseTupleAndKeywords: do basic sanity checks on the arguments,

and raise an error if they're insane.
vgetargskeywords:  the same, except that since this is an internal routine,
just assert that the arguments are sane.

Python/getargs.c

@@ -1005,7 +1005,16 @@ PyArg_ParseTupleAndKeywords(PyObject *args,
 {
 	int retval;
 	va_list va;
-	
+
+	if ((args == NULL || !PyTuple_Check(args)) ||
+	    (keywords != NULL && !PyDict_Check(keywords)) ||
+	    format == NULL ||
+	    kwlist == NULL)
+	{
+		PyErr_BadInternalCall();
+		return -1;
+	}
+
 	va_start(va, kwlist);
 	retval = vgetargskeywords(args, keywords, format, kwlist, &va);	
 	va_end(va);
@@ -1029,6 +1038,12 @@ vgetargskeywords(PyObject *args, PyObject *keywords, char *format,
 	int nkwds, pos, match, converted;
 	PyObject *key, *value;
 
+	assert(args != NULL && PyTuple_Check(args));
+	assert(keywords == NULL || PyDict_Check(keywords));
+	assert(format != NULL);
+	assert(kwlist != NULL);
+	assert(p_va != NULL);
+
 	/* nested tuples cannot be parsed when using keyword arguments */
 
 	for (;;) {