class_docstr: Random mask tokens from src sentence.
code: def __init__(self, opts):
      super().__init__(opts)
  
imports: import random
  import numpy
  from onmt.constants import DefaultTokens
  from onmt.transforms import register_transform
  from .transform import Transform, ObservableStats
label_desc: Use image node_id 1 to create a new TokenMaskTransform object from inherited base classes: HammingDistanceSamplingTransform with example: obj = TokenMaskTransform(opts)