fix: ensure open attribute of Connection never fails

in case the openSession takes long, the initialisation of the session
will not complete immediately. This could make the session attribute
inaccessible. If the Connection is deleted in this time, the open()
check will throw because the session attribute does not exist. Thus, we
default to the Connection being closed in this case. This was not an
issue before because open was a direct attribute of the Connection
class. Caught in the integration tests.

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/client.py

@@ -19,8 +19,6 @@
     OperationalError,
     SessionAlreadyClosedError,
     CursorAlreadyClosedError,
-    Error,
-    NotSupportedError,
 )
 from databricks.sql.thrift_api.TCLIService import ttypes
 from databricks.sql.backend.thrift_backend import ThriftDatabricksClient
@@ -344,7 +342,9 @@ def get_protocol_version(openSessionResp):
     @property
     def open(self) -> bool:
         """Return whether the connection is open by checking if the session is open."""
-        return self.session.open
+        # NOTE: we have to check for the existence of session in case the __del__ is called
+        # before the session is instantiated
+        return hasattr(self, "session") and self.session.open
 
     def cursor(
         self,