code: def get_ploidy(items, region=None):
      
      chrom = chromosome_special_cases(region[0] if isinstance(region, (list, tuple))
                                       else None)
      ploidy = _configured_ploidy(items)
      sexes = _configured_genders(items)
      if chrom == "mitochondrial":
          # For now, do haploid calling. Could also do pooled calling
          # but not entirely clear what the best default would be.
          return ploidy.get("mitochondrial", 1)
      elif chrom == "X":
          # Do standard diploid calling if we have any females or unspecified.
          if "female" in sexes or "f" in sexes:
              return ploidy.get("female", ploidy["default"])
          elif "male" in sexes or "m" in sexes:
              return ploidy.get("male", 1)
          else:
              return ploidy.get("female", ploidy["default"])
      elif chrom == "Y":
          # Always call Y single. If female, filter_vcf_by_sex removes Y regions.
          return 1
      else:
          return ploidy["default"]
docs: Retrieve ploidy of a region, handling special cases.