class_docstr: The API that creates an empty module for later mutations.
  For advanced usages only.
class_docstr_tok: ["The","API","that","creates","an","empty","module","for","later","mutations",".","For","advanced","usages","only","."]
docstr: Forward of placeholder is not meaningful.
  It returns input directly.
docstr_tok: ["Forward","of","placeholder","is","not","meaningful",".","It","returns","input","directly","."]
code: def forward(self, x):
      """
      Forward of placeholder is not meaningful.
      It returns input directly.
      """
      return x
  
imports: import functools
  import warnings
  from typing import Any, Iterator, List, Optional, Dict, Union, Tuple, cast
  from typing_extensions import Literal
  import torch
  import torch.nn
  from nni.mutable import Categorical, CategoricalMultiple, Sample, SampleValidationError, ensure_frozen
  from .base import MutableModule, recursive_freeze
label_desc: Use image node_id 2 for calling the MutationAnchor obj's underlying member method code with example usage: obj.forward(x) and returns: x