code: def op_signature_def(op, key):
      """Creates a signature def with the output pointing to an op.
  
      Note that op isn't strictly enforced to be an Op object, and may be a Tensor.
      It is recommended to use the build_signature_def() function for Tensors.
  
      Args:
        op: An Op (or possibly Tensor).
        key: Key to graph element in the SignatureDef outputs.
  
      Returns:
        A SignatureDef with a single output pointing to the op.
      """
      # Use build_tensor_info_from_op, which creates a TensorInfo from the element's
      # name.
      return build_signature_def(
          outputs={key: utils.build_tensor_info_from_op(op)}
      )
  
imports: from tensorflow.core.framework import types_pb2
  from tensorflow.core.protobuf import meta_graph_pb2
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor
  from tensorflow.python.framework import tensor_util
  from tensorflow.python.saved_model import signature_constants
  from tensorflow.python.saved_model import utils_impl
  from tensorflow.python.util import deprecation
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 12 for calling a global function with example usage: op_signature_def(op, key) and returns: build_signature_def