Can't multiply sequence by non-int of type 'float' in Python -

i have following code in python:

class totalcost:       #constructor       def __init__(self, quantity, size):        self.__quantity=quantity        self.__size=size        self.__cost=0.0        self.__total=0.0       def determinecost(self):         #determine cost per unit        if self.__size=="a":            self.__cost=2.29        elif self.__size=="b":            self.__cost=3.50        elif self.__size=="c":            self.__cost=4.95        elif self.__size=="d":            self.__cost=7.00        elif self.__size=="e":            self.__cost=9.95     def determinetotal(self): #calculate total        self.__total= self.__cost * self.__quantity     def getcost(self):        return self.__cost       def gettotal(self):        return self.__total       def menu(self):        print("----------------sizes/prices----------------")        print("               size = $2.92")        print("               size b = $3.50")        print("               size c = $4.95")        print("               size d = $7.00")        print("               size e = $9.95")        print("--------------------------------------------")     def main():      again=""      print("prices:")      while again!="no":         size=""         quantity=0         display="" #i put variable because wont go without , idk else do>.<         totalcost.menu(display)         while size!="a" , size!="b" , size!="c" , size!="d" , size!="e":             size=str(input("which size? please enter a,b,c,d, or e. : "))         quantity=int(input("how many of size? : "))         while quantity<0:             quantity=int(input("how many of size? : "))         calc=totalcost(size, quantity)           calc.determinecost()         calc.determinetotal()         print("--------------------------------------------")         print("your order:")         print("size: " , size)         print("quantity: " , quantity)         print("cost each: $" , calc.getcost())        print("total cost: $", calc.gettotal())      main()   

i receive following error when execute code:

file "c:/python33/halpmeanon.py", line 21, in determinetotal self._total= self._cost * self.__quantity typeerror: can't multiply sequence non-int of type 'float'

context

this program supposed ask letter(size) & quantity, determine cost per unit given letter, , calculate/output total cost.

how can resolve error in code?

you got order of arguments wrong way round in

calc=totalcost(size, quantity)   

your constructor is:

  def __init__(self, quantity, size): 

a great way code can make sure doesn't happen name arguments when calling method:

instead of:

calc=totalcost(size, quantity) 

do this:

calc=totalcost(size=size, quantity=quantity) # or totalcost(quantity=quantity, size=size) 

that way can give arguments out of order , not have worry bugs 1 encountered.