code: def fetch(cls, obj, keys):
          
          current = obj
          for key in keys.split("."):
              if type(current) == list:
                  try:
                      key = int(key)
                  except TypeError:
                      raise cls.Missing(key)
  
              try:
                  current = current[key]
              except (IndexError, KeyError, TypeError) as ex:
                  raise cls.Missing(key)
  
          return current
docs: fetches the value corresponding to keys from obj