def create_enqueue_op(self):
    """Create the op to enqueue the recorded host_calls.

    Returns:
      A list of enqueue ops, which is empty if there are no host calls.
    """
    if not self._names:
      return []

    tensors = []
    # TODO(jhseu): Consider deduping tensors.
    for name in self._names:
      tensors.extend(self._tensors[name])

    with ops.device(tpu.core(0)):
      return [tpu_ops.outfeed_enqueue_tuple(tensors)]
Create the op to enqueue the recorded host_calls.

    Returns:
      A list of enqueue ops, which is empty if there are no host calls.
    
src/tpu_estimator.py