human
Complete the below
def filter_roidb(roidb):

    ''''Remove roidb entries that have no usable RoIs.'
    '''

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Give me a the Python code you requested?
assistant
#Here is the Python code you requested.
    def is_valid(entry):
        overlaps = entry['max_overlaps']
        fg_inds = np.where((overlaps >= cfg.TRAIN.FG_THRESH))[0]
        bg_inds = np.where(((overlaps < cfg.TRAIN.BG_THRESH_HI) & (overlaps >= cfg.TRAIN.BG_THRESH_LO)))[0]
        valid = ((len(fg_inds) > 0) or (len(bg_inds) > 0))
        return valid
    num = len(roidb)
    filtered_roidb = [entry for entry in roidb if is_valid(entry)]
    num_after = len(filtered_roidb)
    print('Filtered    {}    roidb    entries:    {}    ->    {}'.format((num - num_after), num, num_after))
    return filtered_roidb