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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ListGrrUsers(self):
 """Lists all registered GRR users."""


    args = user_management_pb2.ApiListGrrUsersArgs()

    items = self._context.SendIteratorRequest("ListGrrUsers", args)
    return utils.MapItemsIterator(
        lambda data: GrrUser(data=data, context=self._context), items)