x = input("Please input expression:") lst x.split(" ") print(lst) op = lst[1] x = int(lst[0]) y = int(lst[2]) while len(lst) >=3: if op in ['+',"-","*","/"]: if op == "+": result = x + y if op == "-": result = x - y if op == "*": result = x * y if op == "/": result = x / y print ("the answer is :" , result) for i in range(2): del lst[0] print (lst) op = lst[1] y = int(lst[2]) x = result else : print("operator error")