迭代器协议

2.2 新版功能.

迭代器有两个函数。

int PyIter_Check(PyObject *o)

返回 true ， 如果对象 o 支持迭代器协议的话。

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.

要为迭代器编写一个一个循环，C代码应该看起来像这样

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 */
}