code: def balance(self):
          
          sin = Decimal("0.00")
          sout = Decimal("0.00")
  
          for t in self.trans:
              if t.amount < Decimal("0.00"):
                  sout += t.amount
              else:
                  sin += t.amount
  
          return sin, sout
docs: Returns a tuple of (total amount deposited, total amount
          withdrawn).