Question

I’m writing a script in Python 2.7 exploring the use of the multithreading and Queue modules. the script just defines two functions, one of which will be started in a thread instance to fill a Queue, and a second one which will be started in a second thread instance to pull something off the Queue. However, I cannot even get this script to execute, as it chokes on one of the function definitions even before it executes. The code snippet with the problem is:

def listenThread(counter):
    while queue.empty() != True:
        try:
            outcome = queue.get()
            print outcome
            counter -=1
            print counter 
        except: 
            return 'queue.get() command loop failing.'

The error message I am getting is:

$ python threading-and-queue-test.py
  File "threading-and-queue-test.py", line 34
    except: 
           ^
IndentationError: unindent does not match any outer indentation level
$

I’ve searched SO and checked the docs for correct formation of the try-except construct, and it seems OK. I had earlier versions of the code (without the try-except ) working, so I am getting suspicious about the text editor, TextWrangler v4.0.1.

Can anyone suggest a debug approach or code correction?
Thanks!
Red

Answer 1

As you have already suspected, it is most likely an indentation error. Your text editor is probably mixing the use of tabs and spaces. Replace all tabs with spaces (or vice versa though the standard in python is 4 spaces) and you should see the error disappear.