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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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