循环输入提示计算器（Python）

Question

So I'm making a tip calculator at the moment. The thing that I am stuck on is where they can input the total amount of the cost. If they input an integer I want it to break out of the loop but if they input something else than an integer, I want it to stay in the loop and tell them to enter an integer. Here is the code that I made for this portion. (Not all the code)

Integer = range(1,10000)




while True:
    while True:
        Cost = raw_input("What was the cost? ")
        Cost = int(Cost)
        if Cost in Integer:
            break
        else:
            pass

The spacing may not look correct but it is in the actual script. I still don't know how to paste the code on here without having to add 4 spaces to every line. Anyway, please let me know what you would do to complete the task I need.

Answer 1

Casting a String object to an int can raise a ValueError exception, however since raw_input() returns a str object you can easily check if it's all digits with isdigit() . The full documentation of the isdigit() is found here

if cost.isdigit():
  cost = int(cost)
  break
else:
  cost = raw_input("What is the cost? ")

That was problem number 1. Problem number 2 you're facing is if Cost in Integer .

This is not how that works, you're probably after if isinstance(cost, int): because you want to check if it's an integer after all (since you're converting it)

and lastly:

You should not use while True , while this is working for you you wont be able to break it since you haven't assigned True to a variable.

outer = True
inner = True

while outer:
  while inner:
    #your code here
    inner = False #now it will break automatically from the inner loop.

Answer 2

Cost = int(Cost) will raise a ValueError if Cost is not a string for an Integer.

as such,

    while True:
        Cost = raw_input("What was the cost? ")
        try:
             Cost = int(Cost)
             break
        except ValueError:
             print("Please enter an Integer for the cost")

as you can see, break will only be executed if the ValueError is not raised.

You should not do this though. What you should do is test for isdigit before casting:

    while True:
        Cost = raw_input("What was the cost? ")
        if Cost.isdigit():
             Cost = int(Cost)
             break
        else:
             print("Please enter an Integer for the cost")

exceptions make control flow be unobvious and should be avoided if possible.