Warn about comparing iterables for equality?

Generally iter(x) == iter(x) is false, so comparing iterators and iterables for equality could often be a bug (or at least pointless). Maybe mypy should warn (at least optionally) about equality comparisons like these that have a high potential to be errors. Here is a list of things that seem suspect:

• Comparing anything == Iterator.
• Comparing anything == Iterable (since Iterator is Iterable).
• Comparing dict.values() for equality (since d.values() != d.values()).

Mypy could recommend using the is operator instead.

I'm not sure if this is worth having. There may be some valid uses of comparing iterables using == instead of is, and it's not clear if this actually is a source of problems for programmers. A small experiment with some large codebase could help answer these questions.

I got this idea from a recent thread at python-dev.

Start by reviewing the proposed cases: equality comparisons with Iterator or Iterable types and dict.values(). The issue suggests a small experiment on a large codebase to measure whether these comparisons are common problems; use those findings to define the warning scope and whether recommending is is appropriate.