code: def parse_require(self, env, keys, defaults={}):
          
  
          for k in keys:
              env[k] = getattr(self.options, k) or env.get(k, None)
  
              if env[k] is None:
                  self.error("config syntax error,"
                             "please set `%s` in your env: %s" % (k, env))
  
              pass
  
          for k, v in defaults.items():
              env.setdefault(k, v)
  
          return env
docs: check and get require config
          :param dict env: user config node
          :param list keys: check keys
              .. note::
  
                  option and key name must be same.
  
          :param dict defaults: default value for keys
          :return: dict.env with verified.
  
  
          .. exception::
  
              will raise `ValueError` when some key missed.