Python Error Handling Without GOTO

Question

I am currently getting user input with this line of code:

qty = int(input("How many of this item should we start with?"))

As one would expect, it throws an error if a value is entered that cannot be converted to INT.

On Error, I would like to prompt "Please enter a whole number" and return to the previous line requesting input. What is the most "Pythonic" way of achieving this?

_"What is the most "Pythonic" way of achieving this?"_ In short: Using a `while` loop with `try/except`. See the link above for more info. — Christian Dean, Oct 12 '17 at 16:46
What have you tried already? Have you googled "user input error handling in python" or something along those lines? — toonarmycaptain, Oct 12 '17 at 16:49

NS0 · Accepted Answer · 2017-10-12T16:54:14.277

2

Probably, the most pythonic way is to do the following

while True:
    try:
        qty = int(input("How many of this item should we start with?"))
        break
    except ValueError:
        pass

edited Oct 12 '17 at 16:54

answered Oct 12 '17 at 16:49

NS0

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Note: The question is tagged for Python 3.x, so `input` is what you want, not `raw_input` (which exists only on Py2). – ShadowRanger Oct 12 '17 at 16:53
Ah ok, updated. – NS0 Oct 12 '17 at 16:54
Does pass bring it back to the prompt again? – NickSentowski Oct 12 '17 at 16:59
1

The prompt is back because the `while` loop keeps running, `pass` tells it to do nothing when it sees the error. – NS0 Oct 12 '17 at 16:59
Fantastic, thank you, this will do exactly what I am looking for. – NickSentowski Oct 12 '17 at 17:00
1

@NickSentowski `pass` does literally nothing. It's used in empty blocks. The while loop brings it back because `break` will be not reached in case of exception. – Shmygol Oct 12 '17 at 17:03

Python Error Handling Without GOTO

1 Answers1