Use this method to send audio files, if you want Telegram clients to display the file as a playable voice
            message. For this to work, your audio must be in an .ogg file encoded with OPUS (other formats may be sent
            as Audio or Document). On success, the sent Message is returned. Bots can currently send voice messages of
            up to 50 MB in size, this limit may be changed in the future.

def send_voice(self, chat_id, voice, duration=None, reply_to_message_id=None, reply_markup=None):
        """
            Use this method to send audio files, if you want Telegram clients to display the file as a playable voice
            message. For this to work, your audio must be in an .ogg file encoded with OPUS (other formats may be sent
            as Audio or Document). On success, the sent Message is returned. Bots can currently send voice messages of
            up to 50 MB in size, this limit may be changed in the future.
        """
        payload = dict(chat_id=chat_id,
                       duration=duration,
                       reply_to_message_id=reply_to_message_id,
                       reply_markup=reply_markup)
        files = dict(voice=open(voice, 'rb'))
        return Message.from_api(self, **self._post('sendVoice', payload, files))