Question

Full script here: http://pastebin.com/d6isrghF

I’ll admit I’m very new to Python so please forgive my stupidity if this is an easy question to answer. The section in question is this:

sourcePath = jobPath
while os.path.basename(sourcePath):
    if os.path.basename(os.path.dirname(sourcePath)).lower() == category.lower():
        break
    else:
        sourcePath = os.path.dirname(sourcePath)
if not os.path.basename(sourcePath):
    print "Error: The download path couldn't be properly determined"
    sys.exit()

jobPath is being fed to the script from sabnzbd and is:

/mnt/cache/.apps/sabnzbd/complete/name.of.folder

category is:

tv

So I guess my question is: why is this failing with the error?

Answer 1

Why it does not work

Your code cannot work because while is executed until os.path.basename(sourcePath) is not evaluated to True, then if statement is called, which (because it looks like: if not os.path.basename(sourcePath)) is obviously evaluated as True and thus the message (your “error”) is shown:

Annotated source code

sourcePath = jobPath

# This is executed until os.path.basename(sourcePath) is evaluated as true-ish:
while os.path.basename(sourcePath):
    if os.path.basename(os.path.dirname(sourcePath)).lower() == category.lower():
        break
    else:
        sourcePath = os.path.dirname(sourcePath)

# Then script skips to the remaining part, because os.path.basename(sourcePath)
# has been evaluated as false-ish (see above)

# And then it checks, whether os.path.basename(sourcePath) is false-ish (it is!)
if not os.path.basename(sourcePath):
    print "Error: The download path couldn't be properly determined"
    sys.exit()

When (and why) it sometimes works

It sometimes works only because category is found in the path, which means while loop will be exited (using break) even despite still meeting criteria (the condition after while keyword: os.path.basename(sourcePath)). Because the condition from while loop is still met (we exited the loop even though it was met), the next statement’s condition (not os.path.basename(sourcePath)) is no longer met and the message (“the error”) is not printed.

Possible solutions

I believe one of the solutions is to add a counter to your code, that will print the error only if in specific number of iterations you will not be able to find what you needed. You can also try to catch “too many recursions” exception (if you will use recursion, of course, but the error will be like this: RuntimeError: maximum recursion depth exceeded).

However, you should redesign it rather to meet your own needs.