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

There are two functions specifically for working with iterators.

int PyIter_Check(PyObject *o)

   Return non-zero if the object *o* supports the iterator protocol,
   and "0" otherwise.  This function always succeeds.

int PyAiter_Check(PyObject *o)

   Returns non-zero if the object 'obj' provides "AsyncIterator"
   protocols, and "0" otherwise.  This function always succeeds.

   New in version 3.10.

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 */
   }

type PySendResult

   The enum value used to represent different results of
   "PyIter_Send()".

   New in version 3.10.

PySendResult PyIter_Send(PyObject *iter, PyObject *arg, PyObject **presult)

   Sends the *arg* value into the iterator *iter*. Returns:

   * "PYGEN_RETURN" if iterator returns. Return value is returned via
     *presult*.

   * "PYGEN_NEXT" if iterator yields. Yielded value is returned via
     *presult*.

   * "PYGEN_ERROR" if iterator has raised and exception. *presult* is
     set to "NULL".

   New in version 3.10.
