code: def locus_id_from_variant(variant):
      """Create a locus ID of form "chr:pos_ref" from a Variant object.
  
      Args:
        variant: a nucleus variant.
  
      Returns:
        str.
      """
      return "{}:{}_{}".format(
          variant.reference_name, variant.start, variant.reference_bases
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import enum
  import math
  from typing import List, NamedTuple, Tuple
  from etils import epath
  from IPython import display
  import numpy
  from PIL import Image
  from PIL import ImageDraw
  from third_party.nucleus.protos import variants_pb2
label_desc: Use image node_id 14 for calling a global function with example usage: locus_id_from_variant(variant) and returns: str