python while loop for an entry of 2 integers seperated by delimiter

Question

I need to be able to accept entries as 3,4 , basically 2 integers seperated by a comma. I need a while loop to keep asking for input until they input it in correct format as 2 numbers. this is my code so far

def main():
    try:
        move = [int(s) for s in input("Select a cell (row,col) > ").split(",")]
    except:
        while move != []#stuck here

    x = move[0]
    y = move[1]



main()

Does this answer your question? [Asking the user for input until they give a valid response](https://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response) — Tomerikoo, Apr 07 '20 at 15:01

Ambitions · Answer 1 · 2020-04-07T15:10:34.663

4

You can do it by this way:

def main():
  print('Enter the two points as comma seperated, e.g. 3,4')
  while True:
    try:
      x, y = map(int, input().split(','))
    except ValueError:
      print('Enter the two points as comma seperated, e.g. 3,4')
      continue
    else:
      break


main()

edited Apr 07 '20 at 15:10

answered Apr 07 '20 at 15:06

Ambitions

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BTW the `strip` is not necessary. `int()` will do it alone. For example, `int(" 3 ")` works just fine and returns the `int` 3 – Tomerikoo Apr 07 '20 at 15:09
@Tomerikoo Thank you, I edited it. I did this mistake because I am used to read from files so that I wrote `strip()` – Ambitions Apr 07 '20 at 15:11
1

I don't think it's a mistake anyway... Just redundant and this way the code is just a bit more easy to read :) – Tomerikoo Apr 07 '20 at 15:12

Code-Apprentice · Accepted Answer · 2020-04-07T15:02:59.607

3

You almost have it. You just need to straighten out a few details. First, if the input fails, you want an empty input:

try:
    move = [int(s) for s in input("Select a cell (row,col) > ").split(",")]
except:
    move = []

Now you want to repeat the input until it is valid. You first need the syntax for a while loop:

while <condition>:
   <body>

Where condition evaluates to a boolean and <body> is the lines to repeat. In this case, you want to repeat the try...except.

def main():
    while move != []:
        try:
            move = [int(s) for s in input("Select a cell (row,col) > ").split(",")]
        except:
            move = []

    x = move[0]
    y = move[1]

When you get stuck on syntax issues like this, I suggest you read the documentation and tutorials at https://python.org. They explain how to correctly write a while loop or try...except and more.

edited Apr 07 '20 at 15:02

answered Apr 07 '20 at 15:00

Code-Apprentice

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UnboundLocalError raised because move isn't defined – SuperStormer Apr 07 '20 at 15:01
What would I define move as before? – Lamar Apr 07 '20 at 15:01
1

@Kamal Yup, I missed a detail. What can you initialize `move` to before the `while` loop so that you guarantee that it repeats at least once? – Code-Apprentice Apr 07 '20 at 15:04
2

@SuperStormer Thanks for the comment. I'm going to let the OP think about how to fix my code for a while before I post the fix. – Code-Apprentice Apr 07 '20 at 15:05
@Code-Apprentice Got it! Thank you very much – Lamar Apr 07 '20 at 15:07
@Kamal What solution did you come up with to fix the error in my code? – Code-Apprentice Apr 07 '20 at 15:40

score 2 · Answer 3 · answered Apr 07 '20 at 15:02

You could do this with a nested function and a recursive call if the input doesn't conform to expectations.

import re


def main():

    def prompt():
        digits = input("Select a cell (row,col) > ")
        if not re.match(r'\d+,\d+', digits):
            print('Error message')
            prompt()
        return digits.split(',')

    move = prompt()

    x = move[0]
    y = move[1]


main()

python while loop for an entry of 2 integers seperated by delimiter

3 Answers3