イテレータプロトコル (iterator protocol)
****************************************

イテレータを扱うための固有の関数は二つあります。

int PyIter_Check(PyObject *o)
    * 次に属します: Stable ABI (バージョン 3.8 より).*

   Return non-zero if the object *o* can be safely passed to
   "PyIter_Next()", and "0" otherwise.  This function always succeeds.

int PyAIter_Check(PyObject *o)
    * 次に属します: Stable ABI (バージョン 3.10 より).*

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

   Added in version 3.10.

PyObject *PyIter_Next(PyObject *o)
    *戻り値: 新しい参照。** 次に属します: Stable ABI.*

   Return the next value from the iterator *o*.  The object must be an
   iterator according to "PyIter_Check()" (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.

イテレータの返す要素にわたって反復処理を行うループを書くと、C のコード
は以下のようになるはずです:

   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()".

   Added in version 3.10.

PySendResult PyIter_Send(PyObject *iter, PyObject *arg, PyObject **presult)
    * 次に属します: Stable ABI (バージョン 3.10 より).*

   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".

   Added in version 3.10.
