What is the function of the decorator "implements_iterator" ?

Question

Werkzeug v0.11 I stduy the source code of Werkzeug ,the class ClosingIterator in file wsgi.py,decorted by function implements_iterator:

wsgi.py

@implements_iterator
class ClosingIterator(object):

    """The WSGI specification requires that all middlewares and gateways
    respect the `close` callback of an iterator.  Because it is useful to add
    another close action to a returned iterator and adding a custom iterator
    is a boring task this class can be used for that::

        return ClosingIterator(app(environ, start_response), [cleanup_session,
                                                              cleanup_locals])

    If there is just one close function it can be passed instead of the list.

    A closing iterator is not needed if the application uses response objects
    and finishes the processing if the response is started::

        try:
            return response(environ, start_response)
        finally:
            cleanup_session()
            cleanup_locals()
    """

I find the define of implements_iterator in file _compat.py:

implements_iterator = _identity

_identity = lambda x: x

the question is : what is the function of implements_iterator ?

Answer 1

Werkzeug targets both Python 2 and Python 3. If you scroll up in compat.py, you can see that implements_iterator is defined for Python 2 as follows:

def implements_iterator(cls):
    cls.next = cls.__next__
    del cls.__next__
    return cls

This allows a class to implement a __next__ method (called just next in Python 2) and work for both Python 2 and 3 without any modifications.