def _aggregate_series_fast(self, obj: Series, func: Callable) -> np.ndarray:
    raise NotImplementedError('This should not be reached; use _aggregate_series_pure_python')
def _aggregate_series_fast(self, obj: Series, func: Callable) -> np.ndarray:
    raise NotImplementedError('This should not be reached; use _aggregate_series_pure_python')