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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_hla_truthset(data):
 """Retrieve expected truth calls for annotating HLA called output. """

    val_csv = tz.get_in(["config", "algorithm", "hlavalidate"], data)
    out = {}
    if val_csv and utils.file_exists(val_csv):
        with open(val_csv) as in_handle:
            reader = csv.reader(in_handle)
            next(reader) # header
            for sample, locus, alleles in (l for l in reader if l):
                out = tz.update_in(out, [sample, locus], lambda x: [x.strip() for x in alleles.split(";")])
    return out