<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def square_batch_region(data, region, bam_files, vrn_files, out_file):
 """Perform squaring of a batch in a supplied region, with input BAMs """

    from bcbio.variation import sentieon, strelka2
    if not utils.file_exists(out_file):
        jointcaller = tz.get_in(("config", "algorithm", "jointcaller"), data)
        if jointcaller in ["%s-joint" % x for x in SUPPORTED["general"]]:
            _square_batch_bcbio_variation(data, region, bam_files, vrn_files, out_file, "square")
        elif jointcaller in ["%s-merge" % x for x in SUPPORTED["general"]]:
            _square_batch_bcbio_variation(data, region, bam_files, vrn_files, out_file, "merge")
        elif jointcaller in ["%s-joint" % x for x in SUPPORTED["gatk"]]:
            gatkjoint.run_region(data, region, vrn_files, out_file)
        elif jointcaller in ["%s-joint" % x for x in SUPPORTED["gvcf"]]:
            strelka2.run_gvcfgenotyper(data, region, vrn_files, out_file)
        elif jointcaller in ["%s-joint" % x for x in SUPPORTED["sentieon"]]:
            sentieon.run_gvcftyper(vrn_files, out_file, region, data)
        else:
            raise ValueError("Unexpected joint calling approach: %s." % jointcaller)
    if region:
        data["region"] = region
    data = _fix_orig_vcf_refs(data)
    data["vrn_file"] = out_file
    return [data]