class_docstr: An nbconvert preprocessor that substitutes one set of HTML data
  output for another, adding annotation to the output as required.
  
  The constructor accepts the notebook format version and a
  substitutions dictionary:
  
  {source_html:(target_html, annotation)}
  
  Where the annotation may be None (i.e. no annotation).
code: def __init__(self, version, substitutions, **kw):
      self.nbversion = version
      self.substitutions = substitutions
      super(Preprocessor, self).__init__(**kw)
  
imports: import ast
  from nbconvert.preprocessors import Preprocessor
label_desc: Use image node_id 1 to create a new Substitute object from inherited base classes: Preprocessor with example: obj = Substitute(version, substitutions)