def get_priority(filter_item):
    """ Internal worker function to return the frame-filter's priority
    from a frame filter object.  This is a fail free function as it is
    used in sorting and filtering.  If a badly implemented frame
    filter does not implement the priority attribute, return zero
    (otherwise sorting/filtering will fail and prevent other frame
    filters from executing).

    Arguments:
        filter_item: An object conforming to the frame filter
                     interface.

    Returns:
        The priority of the frame filter from the "priority"
        attribute, or zero.
    """
    # Do not fail here, as the sort will fail.  If a filter has not
    # (incorrectly) set a priority, set it to zero.
    return getattr(filter_item, "priority", 0)