function to check login status

src/delta_barth/errors.py

@@ -4,3 +4,7 @@ class UnspecifiedRequestType(Exception):
 
 class UnknownApiErrorCode(Exception):
     """exception raised if for a given request a unknown error response code is transmitted"""
+
+
+class ApiConnectionError(Exception):
+    """exception raised if an established connection is needed, but the current session is not connected"""