strip a BED file down to its three necessary columns: chrom start end

def minimize(bed_file):
    """
    strip a BED file down to its three necessary columns: chrom start end
    """
    if not bed_file:
        return bed_file
    else:
        sorted_bed = bt.BedTool(bed_file).cut(range(3)).sort()
        if not sorted_bed.fn.endswith(".bed"):
            return sorted_bed.moveto(sorted_bed.fn + ".bed")
        else:
            return sorted_bed