def _example_short_number_for_cost(region_code, cost):
    """Gets a valid short number for the specified cost category.

    Arguments:
    region_code -- the region for which an example short number is needed.
    cost -- the cost category of number that is needed.

    Returns a valid short number for the specified region and cost
    category. Returns an empty string when the metadata does not contain such
    information, or the cost is UNKNOWN_COST.
    """
    metadata = PhoneMetadata.short_metadata_for_region(region_code)
    if metadata is None:
        return U_EMPTY_STRING
    desc = None
    if cost == ShortNumberCost.TOLL_FREE:
        desc = metadata.toll_free
    elif cost == ShortNumberCost.STANDARD_RATE:
        desc = metadata.standard_rate
    elif cost == ShortNumberCost.PREMIUM_RATE:
        desc = metadata.premium_rate
    else:
        # ShortNumberCost.UNKNOWN_COST numbers are computed by the process of
        # elimination from the other cost categoried.
        pass
    if desc is not None and desc.example_number is not None:
        return desc.example_number
    return U_EMPTY_STRING
Gets a valid short number for the specified cost category.

    Arguments:
    region_code -- the region for which an example short number is needed.
    cost -- the cost category of number that is needed.

    Returns a valid short number for the specified region and cost
    category. Returns an empty string when the metadata does not contain such
    information, or the cost is UNKNOWN_COST.