def set_input_fields(self, input_fields):
        """Given a scalar or ordered list of strings generate JSONPaths
        that describe how to access the values necessary for the Extractor """
        if not (isinstance(input_fields, basestring) or
                isinstance(input_fields, types.ListType)):
            raise ValueError("input_fields must be a string or a list")
        self.input_fields = input_fields
        self.generate_json_paths()
        return self