asyncio: Future.set_exception(exc) should instantiate exc if it is a class.

Lib/asyncio/futures.py

@@ -301,6 +301,8 @@ class Future:
         """
         if self._state != _PENDING:
             raise InvalidStateError('{}: {!r}'.format(self._state, self))
+        if isinstance(exception, type):
+            exception = exception()
         self._exception = exception
         self._state = _FINISHED
         self._schedule_callbacks()

Lib/test/test_asyncio/test_futures.py

@@ -79,6 +79,11 @@ class FutureTests(unittest.TestCase):
         self.assertRaises(asyncio.InvalidStateError, f.set_exception, None)
         self.assertFalse(f.cancel())
 
+    def test_exception_class(self):
+        f = asyncio.Future(loop=self.loop)
+        f.set_exception(RuntimeError)
+        self.assertIsInstance(f.exception(), RuntimeError)
+
     def test_yield_from_twice(self):
         f = asyncio.Future(loop=self.loop)