docs: def reset_defaults(self, config_file):
          """Reset defaults.
          """
          if not exists(config_file):
              err_exit('No such file: %(config_file)s' % locals())
          if not isfile(config_file):
              err_exit('Not a file: %(config_file)s' % locals())
          if not os.access(config_file, os.R_OK):
              err_exit('File cannot be read: %(config_file)s' % locals())
          self.set_defaults(config_file)