parameters: (self, source, name, filename=None)
return_statement: return source
docstring: This method is called before the actual lexing and can be used to
          preprocess the source.  The `filename` is optional.  The return value
          must be the preprocessed source.
docstring_summary: This method is called before the actual lexing and can be used to
          preprocess the source.  The `filename` is optional.  The return value
          must be the preprocessed source.
docstring_tokens: This method is called before the actual lexing and can be used to preprocess the source . The filename is optional . The return value must be the preprocessed source .
function: def preprocess(self, source, name, filename=None):
          """This method is called before the actual lexing and can be used to
          preprocess the source.  The `filename` is optional.  The return value
          must be the preprocessed source.
          """
          return source
function_tokens: def preprocess ( self , source , name , filename = None ) : return source