code: def peek_sample_name(variants_iter):
      """Gets the call_set_name from the first Variant of variants_iter.
  
      Args:
        variants_iter: iterable[nucleus.protos.Variant]. Our source of variants.
  
      Returns:
        tuple of (str, iterable[Variant]). The first element is the call_set_name of
        the first variant of variants_iter, or 'UNKNOWN' if the iterable is empty.
        The second is a new iterable that yields the same elements of variant_iter,
        in the same order, which is necessary to return as we need to peek into
        the original iterator.
      """
      try:
          first = next(variants_iter)
          return first.calls[0].call_set_name, itertools.chain(
              [first], variants_iter
          )
      except StopIteration:
          # No variants, just return a placeholder value.
          return "UNKNOWN", iter([])
  
file_path: deepvariant/deepvariant/labeler/labeled_examples_to_vcf.py
imports: import itertools
  from absl import app
  from absl import flags
  from absl import logging
  from deepvariant import dv_utils
  from deepvariant import dv_vcf_constants
  from third_party.nucleus.io import fasta
  from third_party.nucleus.io import tfrecord
  from third_party.nucleus.io import vcf
  from third_party.nucleus.util import variant_utils
  from third_party.nucleus.util import variantcall_utils
label_desc: Use image node_id 3 for calling a global function with example usage: peek_sample_name(variants_iter) and returns: first,  itertools, str,  iter