code: def create_from_key(cls, oldvalue, key):
      "Raise  if the old value already exists"
      if oldvalue is not None:
          raise AlreadyExistsException('%r already exists' % (oldvalue,))
      return cls.create_from_key(keyf create_from_key(cls, oldvalue, key):
      "Raise  if the old value already exists"
      if oldvalue is not None:
          raise AlreadyExistsException('%r already exists' % (oldvalue,))
      return cls.create_from_key(key)
docs: Raise  if the old value already exists