I don't know enough about the Python internals to give a definitive
answer, but I'm assuming/hoping that there is a single, or at most a
few, places in the interpreter that matches up arguments to formal
parameters, and if there's a discrepency it currently raises TypeError.
PyCall sounds promising :-)
In my experience, it's sprinkled all over the place. For example, here are the pertinent chunks of one of our functions that converts VAX floats to IEEE...
static PyObject *vax_data_floats(PyObject *self, PyObject **args, Py_ssize_t nargs)
{
if (nargs != 2) {
PyErr_Format(PyExc_TypeError, "floats: expected 2 arguments, 'bytes' and 'count'");
return NULL;
}
...
if (!PyLong_Check(py_count)) {
PyErr_Format(PyExc_TypeError, "floats: second argument must be an int");
return NULL;
}
...
if (count*(Py_ssize_t)sizeof(float) > bytes_size) {
PyErr_Format(PyExc_TypeError,
"floats: argument 2 is larger than data (only %d bytes for requested %d floats)",
bytes_size,
count);
return NULL;
}