Iterator Protocol — Python 2.7.18 documentation

This document is for an old version of Python that is no longer supported. You should upgrade and read the Python documentation for the current stable release.

# Iterator Protocol

New in version 2.2.

There are two functions specifically for working with iterators.

int `PyIter_Check`(PyObject *o)

  Return true if the object o supports the iterator protocol.

  This function can return a false positive in the case of old-style classes because those classes always define a `tp_iternext` slot with logic that either invokes a `next()` method or raises a `TypeError`.

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 */
    }