Iterator Protocol
*****************

There are two functions specifically for working with iterators.

int PyIter_Check(PyObject *o)

   Return true if the object *o* supports the iterator protocol.

PyObject* PyIter_Next(PyObject *o)
    *Return value: New reference.*

   Return the next value from the iteration *o*.  The object must be
   an iterator (it is up to the caller to check this).  If there are
   no remaining values, returns "NULL" with no exception set.  If an
   error occurs while retrieving the item, returns "NULL" and passes
   along the exception.

To write a loop which iterates over an iterator, the C code should
look something like this:

   PyObject *iterator = PyObject_GetIter(obj);
   PyObject *item;

   if (iterator == NULL) {
       /* propagate error */
   }

   while (item = PyIter_Next(iterator)) {
       /* do something with item */
       ...
       /* release reference when done */
       Py_DECREF(item);
   }

   Py_DECREF(iterator);

   if (PyErr_Occurred()) {
       /* propagate error */
   }
   else {
       /* continue doing useful work */
   }
