code: def example_key(example):
      """Constructs a key for example based on its position and alleles."""
      variant = example_variant(example)
      alts = example_alt_alleles(example)
      return "{}:{}:{}->{}".format(
          variant.reference_name,
          variant.start + 1,
          variant.reference_bases,
          "/".join(alts),
      )
  
imports: import json
  from typing import Optional
  from absl import logging
  import numpy
  import tensorflow
  from deepvariant.protos import deepvariant_pb2
  from third_party.nucleus.io import sharded_file_utils
  from third_party.nucleus.io import tfrecord
  from third_party.nucleus.protos import variants_pb2
  from tensorflow.core.example import example_pb2
label_desc: Use image node_id 10 for calling a global function with example usage: example_key(example) and returns: str