Python while loop in try except instruction

Question

I have simple code:

def simpleMethod():
    try:
        list_to_app = []                                                                                  
        number_of_a = input('\nHow many a you want to create? ')
        number_of_a = int(number_of_a)
        for i in range(number_of_a):                                                           
            user_a = input('\nPlease type here some track: ')
            list_to_app.append(user_a.lower())                                          
    except ValueError:
        stderr.write('Type error - please provide an integer character')
simpleMethod()

I do not want to use something like while True:... How to make some loop (I think while will be fine in this case) for this kind of flow:

user types non-integer
program shows Type error - please provide an integer character
program goes back to 1. step

This is simple method but I'm stuck.

Why do you not want to use a while loop? That is indeed the easiest way to do this. — Samwise
– Samwise, Commented Mar 9, 2021 at 16:18
Why not "while True"? Is this some homework with questionable restrictions? — Michael Butscher
– Michael Butscher, Commented Mar 9, 2021 at 16:19

Samwise · Accepted Answer · 2021-03-09 17:21:51Z

Add a while True loop to repeat the try block until it can successfully break. You probably also want to return the list you're building so that the caller can access it:

def simpleMethod():
    list_to_app = []  

    while True:
        try:
            number_of_a = input('\nHow many a you want to create? ')
            number_of_a = int(number_of_a)
            break
        except ValueError:
            stderr.write('Type error - please provide an integer character')

    for i in range(number_of_a):                                                           
        user_a = input('\nPlease type here some track: ')
        list_to_app.append(user_a.lower())

    return list_to_app  # no point building a list you don't return!                          

tracks = simpleMethod()

A simpler way to build a list is a comprehension -- you can actually put almost the entire function in a single comprehension statement within that while, since the exception will raise to the outer loop. You might also want to make the function name more descriptive:

from typing import List

def get_user_tracks() -> List[str]:
    """Prompt the user for a list of tracks."""
    while True:
        try:
            return [
                input('\nPlease type here some track: ') 
                for _ in range(int(input('\nHow many a you want to create? ')))
            ]
        except ValueError:
            stderr.write('Type error - please provide an integer character')

tracks = get_user_tracks()

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