def alt_bases_from_indices(alt_allele_indices, alternate_bases):
  """Get alt allele bases based on their indices.

  e.g. one alt allele: [0], ["C"] => "C"
  or with two alt alleles: [0,2], ["C", "TT", "A"] => "C-A"

  Args:
    alt_allele_indices: list of integers. Indices of the alt alleles for a
      particular example.
    alternate_bases: list of strings. All alternate alleles for the variant.

  Returns:
    str. Alt allele(s) at the indices, joined by '-' if more than 1.
  """
  alleles = [alternate_bases[i] for i in alt_allele_indices]
  # Avoiding '/' to support use in file paths.
  return '-'.join(alleles)