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PATH: usr / share / doc / python-docs-2.7.5 / html / _sources / c-api

.. highlightlang:: c

.. _iterator:

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

.. versionadded:: 2.2

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

.. c:function:: int PyIter_Check(PyObject *o)

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

.. c:function:: 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 */
   }

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