code: def add_flow_exception(exc):
    
    global _flow_exceptions
    if not isinstance(exc, type) or not issubclass(exc, Exception):
      raise TypeError('Expected an Exception subclass, got %r' % (exc,))
    as_set = set(_flow_exceptions)
    as_set.add(exc)
    _flow_exceptions = tuple(as_set)
docs: Add an exception that should not be logged.
  
    The argument must be a subclass of Exception.