code: def format_alleles(variant):
      """Gets a string representation of the variant's alleles.
  
      Args:
        variant: nucleus.genomics.v1.Variant.
  
      Returns:
        A string ref_bases/alt1,alt2 etc.
      """
      return "{}/{}".format(
          variant.reference_bases, ",".join(variant.alternate_bases)
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import enum
  import itertools
  import six
  from third_party.nucleus.protos import variants_pb2
  from third_party.nucleus.util import ranges
  from third_party.nucleus.util import variantcall_utils
  from third_party.nucleus.util import vcf_constants
label_desc: Use image node_id 7 for calling a global function with example usage: format_alleles(variant) and returns: str