code: def available_configuration_files(self):
          
          known_files = [GLOBAL_CONFIG, LOCAL_CONFIG, self.environment.get('PIP_ACCEL_CONFIG')]
          absolute_paths = [parse_path(pathname) for pathname in known_files if pathname]
          return [pathname for pathname in absolute_paths if os.path.isfile(pathname)]
docs: A list of strings with the absolute pathnames of the available configuration files.