cpython/Doc/c-api/iter.rst

.. highlightlang:: c

.. _iterator:

Iterator Protocol
=================

There are only a couple of functions specifically for working with iterators.

.. cfunction:: int PyIter_Check(PyObject *o)

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


.. cfunction:: PyObject* PyIter_Next(PyObject *o)

   Return the next value from the iteration *o*.  If the object is an iterator,
   this retrieves the next value from the iteration, and returns *NULL* with no
   exception set if there are no remaining items.  If the object is not an
   iterator, :exc:`TypeError` is raised, or if there is an error in 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 */
   }