def _maybe_append_formatted_extension(numobj, metadata, num_format, number):
    if (numobj.extension is not None and len(numobj.extension) > 0):
        if num_format == PhoneNumberFormat.RFC3966:
            return number + _RFC3966_EXTN_PREFIX + numobj.extension
        else:
            if metadata.preferred_extn_prefix is not None:
                return number + metadata.preferred_extn_prefix + numobj.extension
            else:
                return number + _DEFAULT_EXTN_PREFIX + numobj.extension
    return number
Generates the list of valid ORM lookup operators, taking into account runtime options for
dataset/ETHPy150Open daviddrysdale/python-phonenumbers/python/phonenumbers/phonenumberutil.py/_maybe_append_formatted_extension--crossover with--dataset/ETHPy150Open pivotal-energy-solutions/django-datatable-view/datatableview/columns.py/Column.get_lookup_types