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).
docstr: Given some source html substitute and annotated as applicable
docstr_tok: ["Given","some","source","html","substitute","and","annotated","as","applicable"]
code: def replace(self, src):
      "Given some source html substitute and annotated as applicable"
      for html in self.substitutions.keys():
          if src == html:
              annotation = self.annotation % self.substitutions[src][1]
              return annotation + self.substitutions[src][0]
      return src
  
imports: import ast
  from nbconvert.preprocessors import Preprocessor
label_desc: Use image node_id 3 for calling the Substitute obj's underlying member method code with example usage: obj.replace(src) and returns: src, unknown