code: def _get_vaf(variant, vcf_reader):
      """Gets the VAF (variant allele frequency)."""
      vafs = variantcall_utils.get_format(
          variant_utils.only_call(variant), "VAF", vcf_reader
      )
      return sum(vafs)
  
imports: import collections
  import itertools
  import math
  import numpy
  from third_party.nucleus.util import variant_utils
  from third_party.nucleus.util import variantcall_utils
  from deepvariant import vcf_stats_vis
label_desc: Use image node_id 3 for calling a global function with example usage: _get_vaf(variant, vcf_reader) and returns: sum