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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 external_account_cmd_by_name(self, command_name):
 """ Executes a command on the external account specified by name. @param command_name: The name of the command. @return: Reference to the submitted command. @since: API v16 """

    return self._cmd(command_name, data=self.name, api_version=16)