locate the splicejunction file starting from the alignment directory

def get_splicejunction_file(out_dir, data):
    """
    locate the splicejunction file starting from the alignment directory
    """
    samplename = dd.get_sample_name(data)
    sjfile = os.path.join(out_dir, os.pardir, "{0}SJ.out.tab").format(samplename)
    if file_exists(sjfile):
        return sjfile
    else:
        return None