gistfile1.txt

static void ParseColorsTuple
(
    PyObject * ColorTuple,
    uint32_t * colors /* array of 4 elements */
)
/* parses ColorTuple as a tuple of 4 elements, each in turn being a tuple of
  4 integers (r, g, b, a) each in the range [0 .. 255]. Puts the result as
  Cairo-format pixel values into colors. */
{
  PyObject * TheColors[4] = {0, 0, 0, 0};    
  unsigned int nrcolors, i, j, channel[4];
  nrcolors = PyTuple_Size(ColorTuple);
  if (PyErr_Occurred())
    goto cleanup;

  if (nrcolors > 4)
  {
    nrcolors = 4;
  }

  for (i = 0; i < nrcolors; ++i)
  {
    TheColors[i] = PyTuple_GetItem(ColorTuple, i);
    //I'm not sure if it affects the global PyErr_Occurred state, let's assume that it doesn't
    Py_INCREF(TheColors[i]);
    if (PyErr_Occurred())
      goto cleanup;
  }
        
  for (i = 0; i<nrcolors; ++i)
  {
    for (j = 0; j<4; ++j)
    {
      PyObject * ColorObj = PyTuple_GetItem(TheColors[i], j);
      if (PyErr_Occurred())
        goto cleanup;

        const long chanval = PyInt_AsLong(ColorObj);
        if (PyErr_Occurred())
          goto cleanup;
        if (chanval < 0 || chanval > 255)
        {
          PyErr_SetString
            (
              PyExc_ValueError,
              "colour components must be in [0 .. 255]"
            );
          goto cleanup;
        } 
        channel[(j + 1) % 4] = chanval;        
      } 
      colors[i] =
        channel[0] << 24
          |
        channel[1] << 16
          |
        channel[2] << 8
          |
        channel[3];
    }
  }
  for (; i < 4; ++i)
  {
    /* fill unused entries with transparent colour */
    colors[i] = 0;
  }

cleanup:
  for (i = 0; i < nrcolors; ++i)
  {
    //I hope it can handle NULLs
    Py_DECREF(TheColors[i]);
  } 
}