def METHOD_NAME(self, start_frame: Union[int, None] = None, end_frame: Union[int, None] = None):
    """
    Return the slice of snippets
    Parameters
    ----------
    start_frame: (Union[int, None], optional)
        start sample index, or zero if None. Defaults to None.
    end_frame: (Union[int, None], optional)
        end_sample, or number of samples if None. Defaults to None.
    Returns
    -------
    snippets: slice
        slice of selected snippets
    """
    # must be implemented in subclass
    if start_frame is None:
        init = 0
    else:
        init = np.searchsorted(self._spikestimes, start_frame, side="left")
    if end_frame is None:
        endi = self._spikestimes.shape[0]
    else:
        endi = np.searchsorted(self._spikestimes, end_frame, side="left")
    return slice(init, endi, 1)