code: def load_currency(self, mnemonic: str):
          
          # , base_currency: str <= ignored for now.
          if self.rate and self.rate.currency == mnemonic:
              # Already loaded.
              return
  
          app = PriceDbApplication()
          # TODO use the base_currency parameter for the query #33
          symbol = SecuritySymbol("CURRENCY", mnemonic)
          self.rate = app.get_latest_price(symbol)
          if not self.rate:
              raise ValueError(f"No rate found for {mnemonic}!")
docs: load the latest rate for the given mnemonic; expressed in the base currency