Raymond's replied to my follow-up and made me realize that the `next` property could return a callable and it would be transparent to the caller.
On Sunday, March 31, 2013 1:57:08 PM UTC-4, Byron Ruth wrote: > I submitted this as bug last night: http://bugs.python.org/issue17584 and was > *honored* to be rejected by Raymond Hettinger. However, I would like feedback > on whether my concern (this bug) is justified and clarity if not. > > > > Consider: > > > > ```python > > class A(object): > > def __init__(self): > > self.r = iter(range(5)) > > def __iter__(self): > > return self > > @property > > def next(self): > > return next(self.r) > > ``` > > > > The `next` method is a property, however: > > > > ```python > > from collections import Iterator > > a = A() > > isinstance(a, Iterator) # True > > next(a) # TypeError: 'int' object is not callable > > ``` > > > > I am using `collections.Iterator` as the means to check if the object is an > iterator, however I am not sure if that is _root_ problem here. My > understanding of the iterator protocol is that is assumes the __iter__ and > next *methods* are implemented. In the example, `A.next` is defined as a > property, but is still identified as an iterator. To me, this is incorrect > behavior since it's not conforming to the iterator protocol requirements > (i.e. a `next` method, not a property). > > > > Raymond stated: "The design of ABCs are to check for the existence to > required named; none of them verify the signature." I think I understand > _why_ this is the case.. but I downstream libraries use > `collections.Iterator` to determine if an object _is one_: see > https://github.com/django/django/blob/master/django/utils/itercompat.py#L22-L31 > > > > Who's job is it to check if `next` (and technically `__iter__`) are methods? -- http://mail.python.org/mailman/listinfo/python-list
