[Swig-user] Converting a Python list to pointer

[garyr <ga...@fi...>]

I'm trying to write a wrapper for some C++ code. One of the functions has the 
form:

int SSound::outWrite(int numSamples, double *datap)

To invoke this function from Python as
    ss.outWrite(data)
a typemap is required.

Following the examples in the SWIG documentation I came up with this:

%typemap(in) (self, int arg2, double *datap) {
    if (PySequence_Check($input)) {
        int i;
        $1 = PySequence_Length($input);
        $2 = (double *)malloc(($1+1)*sizeof(double));
        for (i = 0; i < $1; i++) {
            PyObject *o = PySequence_GetItem($input, i);
            if (PyDouble_Check(o))
                $2[i] = PyDouble_AsDouble(PySequence_GetItem($input, i));
            else {
                PyErr_SetString(PyExc_TypeError, "arg1 must contain doubles");
                free($2);
                return NULL;
            }
        }
        $2[i] = 0;
    } else {
        PyErr_SetString)PyExc_TypeError, "not a sequence");
        return NULL;
    }
}
%typemap(freearg) (self, int arg2, double * datap) {
    free((char *) $2);
}

which results in this:
Traceback (most recent call last):
  File "testSSound.py", line 17, in <module>
    rc = ss.outWrite(dat)
TypeError: outWrite() takes exactly 3 arguments (2 given)

I also tried it with the "self" in the typemap statement removed and got the 
same results.
What is wrong with the typemap?

Also, why is the length of the allocated memory $1+1 instead of just $1?