code: def to_download():
      
      first_day = parse(interval_first)
      last_day = parse(interval_last)
      format_change = parse('2010-06-14')
      one_day = datetime.timedelta(1)
      cur_day = first_day
      url_list = []
      while cur_day < last_day:
          fname = filename.format(day=cur_day.strftime("%Y%m%d"))
          if cur_day > format_change:
              cur_day += one_day
              url = base_url.format(year_month=cur_day.strftime("%Y.%m"),
                                    file_day=cur_day.strftime("%Y%m%d"))
          else:
              url = base_url_old.format(year_month=cur_day.strftime("%Y.%m"),
                                        file_day=cur_day.strftime("%Y%m%d"))
              cur_day += one_day
          url_list.append((fname, url))
      return sorted(url_list, key=lambda tup: tup[0], reverse=True)
docs: Build interval of urls to download.
          We always get the first file of the next day.
          Ex: 2013-01-01 => 2013-01-02.0000