How to use the pytelegrambotapi.util.is_string function in pyTelegramBotAPI

def to_dic(self):
        ret = {'type': self.type, 'media': 'attach://' + util.generate_random_token()
               if not util.is_string(self.media) else self.media}
        if self.caption:
            ret['caption'] = self.caption
        if self.parse_mode:
            ret['parse_mode'] = self.parse_mode
        if self.width:
            ret['width'] = self.width
        if self.height:
            ret['height'] = self.height
        if self.duration:
            ret['duration'] = self.duration
        if self.supports_streaming:
            ret['supports_streaming'] = self.supports_streaming
        return ret

def add_sticker_to_set(token, user_id, name, png_sticker, emojis, mask_position):
    method_url = 'addStickerToSet'
    payload = {'user_id': user_id, 'name': name, 'emojis': emojis}
    files = None
    if not util.is_string(png_sticker):
        files = {'png_sticker': png_sticker}
    else:
        payload['png_sticker'] = png_sticker
    if mask_position:
        payload['mask_position'] = mask_position.to_json()
    return _make_request(token, method_url, params=payload, files=files, method='post')

def send_data(token, chat_id, data, data_type, reply_to_message_id=None, reply_markup=None, parse_mode=None,
              disable_notification=None, timeout=None, caption=None):
    method_url = get_method_by_type(data_type)
    payload = {'chat_id': chat_id}
    files = None
    if not util.is_string(data):
        files = {data_type: data}
    else:
        payload[data_type] = data
    if reply_to_message_id:
        payload['reply_to_message_id'] = reply_to_message_id
    if reply_markup:
        payload['reply_markup'] = _convert_markup(reply_markup)
    if parse_mode and data_type == 'document':
        payload['parse_mode'] = parse_mode
    if disable_notification:
        payload['disable_notification'] = disable_notification
    if timeout:
        payload['connect-timeout'] = timeout
    if caption:
        payload['caption'] = caption
    return _make_request(token, method_url, params=payload, files=files, method='post')

def send_voice(token, chat_id, voice, caption=None, duration=None, reply_to_message_id=None, reply_markup=None,
               parse_mode=None, disable_notification=None, timeout=None):
    method_url = r'sendVoice'
    payload = {'chat_id': chat_id}
    files = None
    if not util.is_string(voice):
        files = {'voice': voice}
    else:
        payload['voice'] = voice
    if caption:
        payload['caption'] = caption
    if duration:
        payload['duration'] = duration
    if reply_to_message_id:
        payload['reply_to_message_id'] = reply_to_message_id
    if reply_markup:
        payload['reply_markup'] = _convert_markup(reply_markup)
    if parse_mode:
        payload['parse_mode'] = parse_mode
    if disable_notification:
        payload['disable_notification'] = disable_notification
    if timeout:

def send_video(token, chat_id, data, duration=None, caption=None, reply_to_message_id=None, reply_markup=None,
               parse_mode=None, supports_streaming=None, disable_notification=None, timeout=None):
    method_url = r'sendVideo'
    payload = {'chat_id': chat_id}
    files = None
    if not util.is_string(data):
        files = {'video': data}
    else:
        payload['video'] = data
    if duration:
        payload['duration'] = duration
    if caption:
        payload['caption'] = caption
    if reply_to_message_id:
        payload['reply_to_message_id'] = reply_to_message_id
    if reply_markup:
        payload['reply_markup'] = _convert_markup(reply_markup)
    if parse_mode:
        payload['parse_mode'] = parse_mode
    if supports_streaming:
        payload['supports_streaming'] = supports_streaming
    if disable_notification:

def send_audio(token, chat_id, audio, caption=None, duration=None, performer=None, title=None, reply_to_message_id=None,
               reply_markup=None, parse_mode=None, disable_notification=None, timeout=None):
    method_url = r'sendAudio'
    payload = {'chat_id': chat_id}
    files = None
    if not util.is_string(audio):
        files = {'audio': audio}
    else:
        payload['audio'] = audio
    if caption:
        payload['caption'] = caption
    if duration:
        payload['duration'] = duration
    if performer:
        payload['performer'] = performer
    if title:
        payload['title'] = title
    if reply_to_message_id:
        payload['reply_to_message_id'] = reply_to_message_id
    if reply_markup:
        payload['reply_markup'] = _convert_markup(reply_markup)
    if parse_mode:

def set_chat_photo(token, chat_id, photo):
    method_url = 'setChatPhoto'
    payload = {'chat_id': chat_id}
    files = None
    if not util.is_string(photo):
        files = {'photo': photo}
    else:
        payload['photo'] = photo
    return _make_request(token, method_url, params=payload, files=files, method='post')