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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 _add_supplemental_bams(data):
 """Add supplemental files produced by alignment, useful for structural variant calling. """

    file_key = "work_bam"
    if data.get(file_key):
        for supext in ["disc", "sr"]:
            base, ext = os.path.splitext(data[file_key])
            test_file = "%s-%s%s" % (base, supext, ext)
            if os.path.exists(test_file):
                sup_key = file_key + "_plus"
                if sup_key not in data:
                    data[sup_key] = {}
                data[sup_key][supext] = test_file
    return data