def get_num_frames_in_event(event):
    """
    Gets the number of frames in an event retrieved from psana at LCLS.

    Psana events are frame-based, and always contain just one frame. This function
    always returns 1.

    NOTE: This function is designed to be injected as a member function into an
    :class:`~onda.utils.data_event.DataEvent` object.

    Arguments:

        event (:class:`~onda.utils.data_event.DataEvent`): an object storing the event
            data.

    Returns:

        int: the number of frames in the event.
    """
    del event
    return 1
