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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:
 async def _send_sysex(self, sysex_command, sysex_data=None):
 """ This is a private utility method. This method sends a sysex command to Firmata. :param sysex_command: sysex command :param sysex_data: data for command :returns : No return value. """

        if not sysex_data:
            sysex_data = []

        # convert the message command and data to characters
        sysex_message = chr(PrivateConstants.START_SYSEX)
        sysex_message += chr(sysex_command)
        if len(sysex_data):
            for d in sysex_data:
                sysex_message += chr(d)
        sysex_message += chr(PrivateConstants.END_SYSEX)

        for data in sysex_message:
            await self.write(data)