code: def deepvariant_header(
      contigs,
      sample_names,
      add_info_candidates=False,
      include_med_dp=True,
  ):
      """Returns a VcfHeader used for writing VCF output.
  
      This function fills out the FILTER, INFO, FORMAT, and extra header information
      created by the DeepVariant pipeline using consistent fields that DeepVariant
      creates. The `contigs` and `sample_names` fields are unique depending on the
      input data used, so are required inputs.
  
      Args:
        contigs: list(ContigInfo). The list of contigs on which variants were
          called.
        sample_names: list(str). The list of samples present in the run.
        add_info_candidates: Adds the 'CANDIDATES' info field for debugging
          purposes.
        include_med_dp: boolean. If True, we will include MED_DP.
  
      Returns:
        A nucleus.genomics.v1.VcfHeader proto with known fixed headers and the given
        samples and contigs populated.
      """
      version = variants_pb2.VcfExtra(
          key="DeepVariant_version", value=DEEP_VARIANT_VERSION
      )
  
      info_fields = [
          vcf_constants.reserved_info_field("END"),
      ]
      formats = [
          vcf_constants.reserved_format_field("GT"),
          vcf_constants.reserved_format_field("GQ"),
          vcf_constants.reserved_format_field("DP"),
          variants_pb2.VcfFormatInfo(
              id=DEEP_VARIANT_MIN_DP_FORMAT,
              number="1",
              type="Integer",
              description="Minimum DP observed within the GVCF block.",
          ),
          vcf_constants.reserved_format_field("AD"),
          variants_pb2.VcfFormatInfo(
              id=DEEP_VARIANT_VAF_FORMAT,
              number="A",
              type="Float",
              description="Variant allele fractions.",
          ),
          vcf_constants.reserved_format_field("PL"),
      ]
      if add_info_candidates:
          info_fields.append(
              variants_pb2.VcfInfo(
                  id="CANDIDATES",
                  number="1",
                  type=vcf_constants.STRING_TYPE,
                  description="pipe-delimited candidate alleles.",
              )
          )
  
      if include_med_dp:
          formats.append(
              variants_pb2.VcfFormatInfo(
                  id=DEEP_VARIANT_MED_DP_FORMAT,
                  number="1",
                  type="Integer",
                  description=(
                      "Median DP observed within the GVCF block "
                      "rounded to the nearest integer."
                  ),
              )
          )
  
      return variants_pb2.VcfHeader(
          fileformat="VCFv4.2",
          filters=[
              vcf_constants.reserved_filter_field(DEEP_VARIANT_PASS),
              variants_pb2.VcfFilterInfo(
                  id=DEEP_VARIANT_REF_FILTER,
                  description="Genotyping model thinks this site is reference.",
              ),
              variants_pb2.VcfFilterInfo(
                  id=DEEP_VARIANT_QUAL_FILTER,
                  description=(
                      "Confidence in this variant being real is below "
                      "calling threshold."
                  ),
              ),
              variants_pb2.VcfFilterInfo(
                  id=DEEP_VARIANT_NO_CALL,
                  description="Site has depth=0 resulting in no call.",
              ),
          ],
          infos=info_fields,
          formats=formats,
          contigs=contigs,
          sample_names=sample_names,
          extras=[version],
      )
  
label_desc: Use image node_id 1 for calling a global function with example usage: deepvariant_header(contigs, sample_names, add_info_candidates, include_med_dp) and returns: variants_pb2