我的初学python项目（计算器）有输入问题

Question

每当我测试我的计算器，看看它如何处理输入不是数字，它会标记一个ValueError。更确切地说，这一个“ValueError：无法将字符串转换为浮点数：'a'”。我试图修改这个，所以有一个解决方案来处理非整数，但无济于事......非常感谢帮助。

这里是我到目前为止的代码：

print("1. ADDITION ") 
print("2. MULTIPLICATION ") 
print("3. TAKEAWAY ") 
print("4. DIVISION ") 

Operator = int(input("please enter one of the numbers above to decide the operator you want. ")) 

while Operator > 4: 
    print("Please select a number from the options above. ") 
    Operator = int(input("please enter one of the numbers above to decide the operator you want. ")) 
    if Operator != (1 or 2 or 3 or 4): 
     print("please enter one of the options above. ") 
     Operator = int(input("please enter one of the numbers above to decide the operator you want. ")) 
    continue 

while True: 
    Num1 = float(input("Please enter first number. ")) 
    if Num1 == float(Num1): 
     print("thanks! ") 
    elif Num1 != float(Num1): 
     Num1 = float(input("Please enter first number. ")) 
    break 

while True: 
    Num2 = float(input("Please enter second number. ")) 
    if Num2 == float(Num2): 
     print("thanks ") 
    elif Num1 != float(Num1): 
     Num1 = float(input("Please enter first number. ")) 
    break 

Answer 1

请阅读文档处理异常：

https://docs.python.org/2/tutorial/errors.html#handling-exceptions

的浮动：

try: 
    x = float(input("Please enter a number: ")) 
    break 
except ValueError: 
    print "Oops! That was no valid number. Try again..." 

Answer 2

异常处理是什么你在找什么。 Smthng这样的：

input = 'a' 
try: 
    int(a) 
except ValueError: 
    print 'Input is not integer' 

Answer 3

注意：应在小写根据PEP8命名变量，请参阅：What is the naming convention in Python for variable and function names?。

如果要重新输入，直到你没有得到ValueError，把它放在一个循环：

print("Please select a number from the options above.") 
while True: 
    try: 
     operator = int(input("please enter one of the numbers above to decide the operator you want: ")) 
    except ValueError: 
     print("Sorry, not a number. Please retry.") 
    else: 
     if 1 <= operator <= 4: 
      break 
     else: 
      print("Sorry, choose a value between 1 and 4.") 

注：使用input与Python 3.x或raw_input与Python 2.7

1. ADDITION 
2. MULTIPLICATION 
3. TAKEAWAY 
4. DIVISION 
Please select a number from the options above. 
please enter one of the numbers above to decide the operator you want: spam 
Sorry, not a number. Please retry. 
please enter one of the numbers above to decide the operator you want: 12 
Sorry, choose a value between 1 and 4. 
please enter one of the numbers above to decide the operator you want: 2