def get_photo_url(photo_id):
args = _get_request_args(<EOL>'<STR_LIT>',<EOL>photo_id=photo_id<EOL>)<EOL>resp = requests.post(API_URL, data=args)<EOL>resp_json = json.loads(resp.text.encode('<STR_LIT:utf-8>'))<EOL>logger.debug(json.dumps(resp_json, indent=<NUM_LIT:2>))<EOL>size_list = resp_json['<STR_LIT>']['<STR_LIT:size>']<EOL>size_list_len = len(size_list)<EOL>global image_size_mode<EOL>image_size_mode = size_list_len if size_list_len < image_size_modeelse image_size_mode<EOL>download_url = resp_json['<STR_LIT>']['<STR_LIT:size>'][-image_size_mode]['<STR_LIT:source>']<EOL>return download_url<EOL>
Request the photo download url with the photo id
    :param photo_id: The photo id of flickr
    :type photo_id: str
    :return: Photo download url
    :rtype: str