Add TODOs

src/python/grpcio/grpc/_channel.py

@@ -331,6 +331,8 @@ class _SingleThreadedRendezvous(grpc.RpcError, grpc.Call):  # pylint: disable=to
             _common.wait(self._state.condition.wait, _done)
             return self._state.trailing_metadata
 
+    # TODO(https://github.com/grpc/grpc/issues/20763): Drive RPC progress using
+    # the calling thread.
     def code(self):
         """See grpc.Call.code"""
         with self._state.condition:

src/python/grpcio_tests/tests/unit/_metadata_test.py

@@ -202,8 +202,8 @@ class MetadataTest(unittest.TestCase):
     def testUnaryStream(self):
         multi_callable = self._channel.unary_stream(_UNARY_STREAM)
         call = multi_callable(_REQUEST, metadata=_INVOCATION_METADATA)
-        # NOTE(gnossen): In the single-threaded case, we must consume at least
-        # one message before the initial metadata will show up.
+        # TODO(https://github.com/grpc/grpc/issues/20762): Make the call to
+        # `next()` unnecessary.
         next(call)
         self.assertTrue(
             test_common.metadata_transmitted(_EXPECTED_INITIAL_METADATA,