Writing a Python C extension: how to correctly load a PyListObject?
static PyObject *orbital_spectra(PyObject *self, PyObject *args) {
  PyListObject *input = (PyListObject*)PyList_New(0);
  real channels[7], coefficients[7], values[240];
  int i;

  if (!PyArg_ParseTuple(args, "O!", &PyList_Type, &input)) {
    return NULL;
  }
  for (i = 0; i < PyList_Size(input); i++) {
    printf("%fn", PyList_GetItem(input, (Py_ssize_t)i)); // <--- Prints zeros
  }
//....
}

printf("%fn", PyFloat_AsDouble(PyList_GetItem(input, (Py_ssize_t)i)));