Python迭代器协议在迭代器返回值中？

因此，我最近在python类中了解了迭代器协议，并且我被告知

\uuuuiter\uuuuuuuuuuuuuuuuuuuuuuself）

方法应该始终返回一个新的迭代器，而不是

self

。在流畅的Python书中，它谈到在迭代器中返回

self

，因此我不确定为什么我的导师告诉我不能使用self作为返回值

这是我们在考试中遇到的一个例子，我因为使用self而不是FileName迭代器而丢了分数

class FileNamesIterator:
    """
    Iterator that iterates over all the file names in the
    FileNamesIterable.
    """

    def __init__(self, filename_iterable: FileNamesIterable):
        self.filename_iterable = filename_iterable
        self.curr_index = 0

    def __next__(self) -> str:
        file_list = self.filename_iterable.file_list
        if self.curr_index == len(file_list):
            raise StopIteration()

        next_file_name = file_list[self.curr_index]
        self.curr_index += 1

        if ".png" in next_file_name:
            next_file_name = f"{next_file_name} - Portable Network Graphics " \
                             f"File"
        elif ".gif" in next_file_name:
            next_file_name = f"{next_file_name} - Graphics Interchange " \
                             f"Format File"

        return next_file_name

    def __iter__(self) -> FileNamesIterator:
        return self


class FileNamesIterable:
    def __init__(self, file_list: list):
        self.file_list = file_list

    def __iter__(self) -> FileNamesIterator:
        return FileNamesIterator(self)

---

要在容器类中实现迭代器协议，需要向其添加一个

\uuuu iter\uuu

方法。这允许使用

for

循环对类实例进行迭代，因为它在类实例上调用

iter（）

，以获取迭代器对象（从

实例中）。然后从返回的对象（迭代器）调用
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu（提升
StopIteration
，而不是返回另一个数据值）。这就是迭代器类的
\uuuIter\uuuuuuuuuuuuuu
方法应使用
\uuuuuuuuuuuuu
方法返回对象的原因

如果实现协议的类本身可以有
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu

class MyIterator:
    def __init__(self, data):
        self._data = data
        self._index = 0

    def __next__(self):
        if self._index == len(self._data):
            raise StopIteration
        self._index += 1
        return self._data[self._index-1]

    def __iter__(self):
        return self

如果将迭代器类与iterable对象分开，则必须返回新的迭代器对象，而不是
self
（也不是迭代器类名）：

输出：

Using a single class:
<__main__.MyIterator object at 0x7f65a23b6fd0>
1
2
3

Separating the iterator class from the container class:
<__main__.Iterator object at 0x7f65a23b6ca0>
1
2
3

使用单个类：
1.
2.
3.
将迭代器类与容器类分离：
1.
2.
3.

Using a single class:
<__main__.MyIterator object at 0x7f65a23b6fd0>
1
2
3

Separating the iterator class from the container class:
<__main__.Iterator object at 0x7f65a23b6ca0>
1
2
3