I want to run a loop in my script while the user has not input anything. But when they have input something I want the loop to break.

The issue I am currently having is that when using the input() function, the script will stop and wait for an input, but I want to run another part of the script while waiting for the user input.

I have tried using try: with a raw_input():

while True:
    try:
        print('SCAN BARCODE')
        userInput= raw_input()
        #doing something with input
    except:
        #run this while there is no input

With this, I find that whatever is in the except: will always run, but it will not run try: even when there is a user input. If I change raw_input() to input() the script just waits at input() and doesn't run anything in the except:.

How do I achieve what I am after?