code: def _tstv(variant, vtype):
      """Returns a pair of bools indicating Transition, Transversion status."""
      if vtype == BIALLELIC_SNP:
          is_transition = variant_utils.is_transition(
              variant.reference_bases, variant.alternate_bases[0]
          )
          is_transversion = not is_transition
      else:
          is_transition = is_transversion = False
  
      return is_transition, is_transversion
  
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 2 for calling a global function with example usage: _tstv(variant, vtype) and returns: is_transition,  is_transversion