class_docstr: Add Prefix to src (& tgt) sentence.
code: def __init__(self, opts):
      super().__init__(opts)
  
imports: from onmt.utils.logging import logger
  from onmt.transforms import register_transform
  from .transform import Transform, ObservableStats
label_desc: Use image node_id 1 to create a new PrefixTransform object from inherited base classes: Transform with example: obj = PrefixTransform(opts)