For example, the following code is illegal in Python 3 (implementing __eq__ shadows your __hash__ implementation with None in Python 3)

class Foo(object):
  def __init__(self, x):
    self.x = x
  def __eq__(self, other):
    if not isinstance(other, Foo):
      return NotImplemented
    return self.x == other.x

set_of_foo = {Foo(1), Foo(2)}

Poking around the code, AFAICT mypy doesn't do any Hashable checks. I don't see any other Protocols being checked in checker.py. Is there any existing tickets around supporting Protocols in mypy?