code: def extractParamMap(self, extra=None):
          
          if extra is None:
              extra = dict()
          paramMap = self._defaultParamMap.copy()
          paramMap.update(self._paramMap)
          paramMap.update(extra)
          return paramMap
docs: Extracts the embedded default param values and user-supplied
          values, and then merges them with extra values from input into
          a flat param map, where the latter value is used if there exist
          conflicts, i.e., with ordering: default param values <
          user-supplied values < extra.
  
          :param extra: extra param values
          :return: merged param map