code: def set_output_fields(self, output_fields):
          
          if isinstance(output_fields, dict) or isinstance(output_fields, list):
              self.output_fields = output_fields
          elif isinstance(output_fields, basestring):
              self.output_field = output_fields
          else:
              raise ValueError("set_output_fields requires a dictionary of "
                               + "output fields to remap, a list of keys to filter, or a scalar string")
          return self
docs: Defines where to put the dictionary output of the extractor in the doc, but renames
          the fields of the extracted output for the document or just filters the keys