class_docstr: Environment Variable Placeholder helps access EnvironmentVariable proto.
  
  Prefer to use environment_variable(...) to create Environment Variable
  placeholder.
class_docstr_tok: ["Environment","Variable","Placeholder","helps","access","EnvironmentVariable","proto",".","Prefer","to","use","environment_variable","(","...",")","to","create","Environment","Variable","placeholder","."]
docstr: Initializes the class. Consider this private.
docstr_tok: ["Initializes","the","class",".","Consider","this","private","."]
code: def __init__(self, key: str):
      """Initializes the class. Consider this private."""
      super().__init__(expected_type=placeholder_base.ValueType)
      self._key = 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 1 to create a new EnvironmentVariablePlaceholder object from inherited base classes: placeholder_base with example: obj = EnvironmentVariablePlaceholder(key)