How do I avoid error while using int()?

Question

I have a question concerning int(). Part of my Python codes looks like this

string = input('Enter your number:')
n = int(string)
print n

So if the input string of int() is not a number, Python will report ValueError and stop running the remaining codes.

I wonder if there is a way to make the program re-ask for a valid string? So that the program won't just stop there.

Thanks!

Possible duplicate: http://stackoverflow.com/questions/5424716/how-to-check-if-string-input-is-a-number — Phillip K, May 12 '17 at 06:42
Possible duplicate of [How to check if string input is a number?](http://stackoverflow.com/questions/5424716/how-to-check-if-string-input-is-a-number) — Chiheb Nexus, May 12 '17 at 06:45

itzMEonTV · Answer 1 · 2017-05-12T07:15:26.133

2

You can use try except

while True:
    try:
        string = input('Enter your number:')
        n = int(string)
        print n
        break
    except ValueError:
        pass

edited May 12 '17 at 07:15

answered May 12 '17 at 06:42

itzMEonTV

19,851
4
39
49

You are missing a `break` somewhere :p – Imanol Luengo May 12 '17 at 06:45
You are missing a `:` too. Also, you should try to avoid infinite while loops and give them a clever condition instead. – FMaz May 12 '17 at 07:07
Updated. Thank you both :) – itzMEonTV May 12 '17 at 07:16

score 1 · Answer 2 · answered May 12 '17 at 06:41

1

Put the whole thing in an infinite loop. You should catch and ignore ValueErrors but break out of the loop when you get a valid integer.

answered May 12 '17 at 06:41

Noufal Ibrahim

71,383
13
135
169

score 0 · Answer 3 · answered May 12 '17 at 06:43

0

n = None
while not isinstance(n, int):
    try:
        n = int(input('Enter your number:'))
    except:
        print('NAN')

answered May 12 '17 at 06:43

Vetsin

2,245
1
20
24

You are catching a very broad exception. Somehow input console is corrupted that will stuck in a infinite loop. – Adnan Umer May 12 '17 at 12:42

score 0 · Accepted Answer · answered May 12 '17 at 06:44

0

What you're looking for is

Try / Except

How it works:

try:
    # Code to "try".
except:
    # If there's an error, trap the exception and continue.
    continue

For your scenario:

def GetInput():
    try:
        string = input('Enter your number:') 
        n = int(string) 
        print n
    except:
        # Try to get input again.
        GetInput()

answered May 12 '17 at 06:44

Joe

159
3
14

This `GetInput` function does not return anything useful. – VPfB May 12 '17 at 18:46

score 0 · Answer 5 · answered May 12 '17 at 07:06

While the others have mentioned that you can use the following method,

try :
except :

This is another way to do the same thing.

while True : 
    string = input('Enter your number:')
    if string.isdigit() : 
        n = int(string)
        print n
        break
     else : 
        print("You have not entered a valid number. Re-enter the number")

You can learn more about Built-in String Functions from here.

How do I avoid error while using int()?

5 Answers5

Try / Except