Python: location of py/iter-returns-non-iterator can be confusing

[s0]

See https://discuss.lgtm.com/t/python-false-positive-the-iter-method-of-iterable-class-xxx-does-not-return-an-iterator/2116

In the case where __iter__ returns an instance of a class that partially implements an iterator (e.g. implements __next__ but not __iter__), then the alert location and message can be confusing, as the problem actually lies with the definition of the iterator, and not the use of it.

As a suggested improvement, when returning an instance of a class that implements __next__ but not __iter__, the alert location should instead be the iterator class, and the message something like "This class is returned as an iterator {here}, but is missing a definition for __next__, so does not fully implement the iterator interface."

[webknjaz]

Not sure how relevant this is here but this check may also need to take into account the fact that projects can have hybrid Python support, meaning that the code is written in a subset of Python which both Python 2 and Python 3 can interpret perfectly.
In such a case, an iterator can implement one of __next__ or next but not both which can make this check flaky as it'd work only under one of Python branches and the linter can miss it if it'd guess the wrong branch...