code: def _init_flow_exceptions():
    
    global _flow_exceptions
    _flow_exceptions = ()
    add_flow_exception(datastore_errors.Rollback)
    try:
      from webob import exc
    except ImportError:
      pass
    else:
      add_flow_exception(exc.HTTPException)
docs: Internal helper to initialize _flow_exceptions.
  
    This automatically adds webob.exc.HTTPException, if it can be imported.