Also wird im Fehlerfall nur das addErrBack ausgelöst.
Only in case of an error, addErrBack is tiggered.
After he wrote that dhwz gave the tumbs-up. Earlier dhwz pointed to this document: Twisted document
addErrBack looks to me to kind of lighting rod that takes the error so the script can continue. But then I am not a programmer.
In a earlier posting by dhwz: posting by dhwz