Improve error message when await_ call errors

Fixes: #5832
Change-Id: Ia2ed8f1d1ec54e5f6e1a8f817a69446fdb3b7f6d

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/sqlalchemy/exc.py b/lib/sqlalchemy/exc.py
index 08b1bb060..289b8dfab 100644
--- a/lib/sqlalchemy/exc.py
+++ b/lib/sqlalchemy/exc.py
@@ -294,6 +294,15 @@ class AwaitRequired(InvalidRequestError):
     code = "xd1r"
 
 
+class MissingGreenlet(InvalidRequestError):
+    r"""Error raised by the async greenlet await\_ if called while not inside
+    the greenlet spawn context.
+
+    """
+
+    code = "xd2s"
+
+
 class NoReferencedTableError(NoReferenceError):
     """Raised by ``ForeignKey`` when the referred ``Table`` cannot be
     located.