class_docstr: Preprocessor to convert notebooks to Python source to convert use of
  output magic to use the util.output utility instead.
code: def __call__(self, nb, resources):
      return self.preprocess(nb, resources)
  
imports: import ast
  from nbconvert.preprocessors import Preprocessor
label_desc: Use image node_id 2 for calling the OutputMagicProcessor obj's underlying member method code with example usage: obj.__call__(nb, resources) and returns: self