code: def path_regex(self):
          
          try:
              path = '%s/' % urljoin(self.monthly_build_list_regex,
                                     self.builds[self.build_index])
              if self.application in APPLICATIONS_MULTI_LOCALE \
                      and self.locale != 'multi':
                  path = '%s/' % urljoin(path, self.locale)
              return path
          except Exception:
              folder = urljoin(self.base_url, self.monthly_build_list_regex)
              raise errors.NotFoundError("Specified sub folder cannot be found",
                                         folder)
docs: Return the regex for the path to the build folder.