def _chk_fields(field_data, field_formatter):
        """Check that expected fields are present."""
        if len(field_data) == len(field_formatter):
            return
        len_dat = len(field_data)
        len_fmt = len(field_formatter)
        msg = [
            "FIELD DATA({d}) != FORMATTER({f})".format(d=len_dat, f=len_fmt),
            "DAT({N}): {D}".format(N=len_dat, D=field_data),
            "FMT({N}): {F}".format(N=len_fmt, F=field_formatter)]
        raise Exception("\n".join(msg))
Check that expected fields are present.