code: def _example_short_number_for_cost(region_code, 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
docs: 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.