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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 _run_freebayes_caller(align_bams, items, ref_file, assoc_files, region=None, out_file=None, somatic=None):
 """Detect SNPs and indels with FreeBayes. Performs post-filtering to remove very low quality variants which can cause issues feeding into GATK. Breaks variants into individual allelic primitives for analysis and evaluation. """

    config = items[0]["config"]
    if out_file is None:
        out_file = "%s-variants.vcf.gz" % os.path.splitext(align_bams[0])[0]
    if not utils.file_exists(out_file):
        if not utils.file_exists(out_file):
            with file_transaction(items[0], out_file) as tx_out_file:
                freebayes = config_utils.get_program("freebayes", config)
                input_bams = " ".join("-b %s" % x for x in align_bams)
                opts, no_target_regions = _freebayes_options_from_config(items, config, out_file, region)
                if no_target_regions:
                    vcfutils.write_empty_vcf(tx_out_file, config, samples=[dd.get_sample_name(d) for d in items])
                else:
                    opts = " ".join(opts)
                    # Recommended options from 1000 genomes low-complexity evaluation
                    # https://groups.google.com/d/msg/freebayes/GvxIzjcpbas/1G6e3ArxQ4cJ
                    opts += " --min-repeat-entropy 1"
                    # Remove partial observations, which cause a preference for heterozygote calls
                    # https://github.com/ekg/freebayes/issues/234#issuecomment-205331765
                    opts += " --no-partial-observations"
                    if somatic:
                        opts = _add_somatic_opts(opts, somatic)
                    compress_cmd = "| bgzip -c" if out_file.endswith("gz") else ""
                    # For multi-sample outputs, ensure consistent order
                    samples = ("-s" + ",".join([dd.get_sample_name(d) for d in items])) if len(items) > 1 else ""
                    fix_ambig = vcfutils.fix_ambiguous_cl()
                    py_cl = config_utils.get_program("py", config)
                    cmd = ("{freebayes} -f {ref_file} {opts} {input_bams} "
                           """| bcftools filter -i 'ALT="<*>" || QUAL > 5' """
                           "| {fix_ambig} | bcftools view {samples} -a - | "
                           "{py_cl} -x 'bcbio.variation.freebayes.remove_missingalt(x)' | "
                           "vcfallelicprimitives -t DECOMPOSED --keep-geno | vcffixup - | vcfstreamsort | "
                           "vt normalize -n -r {ref_file} -q - | vcfuniqalleles | vt uniq - 2> /dev/null "
                           "{compress_cmd} > {tx_out_file}")
                    do.run(cmd.format(**locals()), "Genotyping with FreeBayes", {})
    return out_file