code: def path_regex(self):
          
          regex = r'%(PREFIX)s%(BUILD)s/%(PLATFORM)s/%(LOCALE)s/'
          return regex % {'PREFIX': self.candidate_build_list_regex,
                          'BUILD': self.builds[self.build_index],
                          'LOCALE': self.locale,
                          'PLATFORM': self.platform_regex}
docs: Return the regex for the path to the build folder.