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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_samtools(align_bams, items, ref_file, assoc_files, region=None, out_file=None):
 """Detect SNPs and indels with samtools mpileup and bcftools. """

    return shared_variantcall(_call_variants_samtools, "samtools", align_bams, ref_file,
                              items, assoc_files, region, out_file)