Python iterators – how to dynamically assign self.next within a new style class?

Question

As part of some WSGI middleware I want to write a python class that wraps an iterator to implement a close method on the iterator.

This works fine when I try it with an

Answer 1

Looks like built-in iter doesn't check for next callable in an instance but in a class and IteratorWrapper2 doesn't have any next. Below is simpler version of your problem

class IteratorWrapper2(object):

    def __init__(self, otheriter):
        self.next = otheriter.next

    def __iter__(self):
        return self

it=iter([1, 2, 3])
myit = IteratorWrapper2(it)

IteratorWrapper2.next # fails that is why iter(myit) fails
iter(myit) # fails

so the solution would be to return otheriter in __iter__

class IteratorWrapper2(object):

    def __init__(self, otheriter):
        self.otheriter = otheriter

    def __iter__(self):
        return self.otheriter

or write your own next, wrapping inner iterator

class IteratorWrapper2(object):

    def __init__(self, otheriter):
        self.otheriter = otheriter

    def next(self):
        return self.otheriter.next()

    def __iter__(self):
        return self

Though I do not understand why doesn't iter just use the self.next of instance.