code: def pop(self, key, default=_sentinel):
          
          if default is not _sentinel:
              tup = self._data.pop(key.lower(), default)
          else:
              tup = self._data.pop(key.lower())
          if tup is not default:
              return tup[1]
          else:
              return default
docs: Removes the specified key and returns the corresponding value.
          If key is not found, the default is returned if given, otherwise KeyError is raised.
  
          :param key: The key
          :param default: The default value
          :return: The value