def each(self, field_names):
field_ids = []<EOL>for f in field_names:<EOL><INDENT>field_ids.append(self.fields.index(f))<EOL><DEDENT>for r in self.results:<EOL><INDENT>yield([r[i] for i in field_ids])<EOL><DEDENT>
Iterate over the results, yielding a list for each result, where
        each element corresponds to the field given in the field_name parameters

        Parameters
        ----------
        field_names: list of str
            The names of the fields to be returned during iteration

        Returns
        -------
        None

        Exceptions
        ----------
        raises something when a field name is not in self.fields