Iterator Protocol — Python v2.6.9 documentation

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# Iterator Protocol

New in version 2.2.

There are only a couple of 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. 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, `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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