class_docstr: An internal wrapper around tuple(token, func).
  
  `token` can be either a single token (if the py_func returns a tensor), or a
  list of tokens (if the py_func returns a list of tensors).
  
  The main purpose of this class is to provides the two methods:
  `from_proto` and `to_proto` that enable storing tuple objects in the graph's
  collections as proto objects.
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code: def to_proto(self, export_scope=None):
      del export_scope  # Unused
      result = attr_value_pb2.AttrValue()
      result.s = dill.dumps(self)
      return result
  
file_path: transform/tensorflow_transform/py_func/pyfunc_helper.py
imports: import dill
  import tensorflow
  from tfx_bsl.types import tfx_namedtuple
  from tensorflow.core.framework import attr_value_pb2
  from tensorflow.python.framework import ops
label_desc: Use image node_id 3 for calling the _PyFuncDef obj's underlying member method code with example usage: obj.to_proto(export_scope) and returns: result