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

def set_output_fields(self, output_fields):
        """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"""
        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