class_docstr: ExecProperty Placeholder represents an execution property.
  
  Prefer to use exec_property(...) to create exec property placeholders.
class_docstr_tok: ["ExecProperty","Placeholder","represents","an","execution","property",".","Prefer","to","use","exec_property","(","...",")","to","create","exec","property","placeholders","."]
code: def key(self) -> str:
      return self._key
  
imports: from __future__ import annotations
  import typing
  from typing import Any, Literal, Optional, Union
  from tfx.dsl.placeholder import placeholder_base
  from tfx.proto.orchestration import placeholder_pb2
  from google.protobuf import message
label_desc: Use image node_id 2 for calling the ExecPropertyPlaceholder obj's underlying member method code with example usage: obj.key() and returns: self