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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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