Allow isinstance checks of TypedDict from the typing module (#2615)

Fixes #2614

Author: rowillia

extensions/mypy_extensions.py

@@ -15,7 +15,7 @@
 
 def _check_fails(cls, other):
     try:
-        if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools']:
+        if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools', 'typing']:
             # Typed dicts are only for static structural subtyping.
             raise TypeError('TypedDict does not support instance and class checks')
     except (AttributeError, ValueError):

mypy/test/testextensions.py

@@ -114,6 +114,12 @@ def test_pickle(self):
             EmpDnew = pickle.loads(ZZ)
             self.assertEqual(EmpDnew({'name': 'jane', 'id': 37}), jane)
 
+    def test_optional(self):
+        EmpD = TypedDict('EmpD', name=str, id=int)
+
+        self.assertEqual(typing.Optional[EmpD], typing.Union[None, EmpD])
+        self.assertNotEqual(typing.List[EmpD], typing.Tuple[EmpD])
+
 
 if __name__ == '__main__':
     main()