Python create directory failing

Question

I am using some pretty standard code:

 1   if not os.path.exists(args.outputDirectory):
 2       if not os.makedirs(args.outputDirectory, 0o666):
 3           sys.exit('Fatal: output directory "' + args.outputDirectory + '" does not exist and cannot be created')

I remove the directory and the check at 1 drops through to 2. I one-step beyond that and hit the error message at 3.

However, when I check, the directory was created successfully.

drwxrwsr-x 2 userId userGroup  4096 Jun 25 16:07 output/

What am I missing??

Answer 1

os.makedirs does not indicate whether it succeeded through its return value: it always returns None.

None is False-y, therefore, not os.makedirs(args.outputDirectory, 0o666) is always True, which triggers your sys.exit code path.

---

Fortunately, you don't need any of that. If os.makedirs fails, it'll throw an OSError.

You should catch the exception, not check the return value:

try:
    if not os.path.exists(args.outputDirectory):
        os.makedirs(args.outputDirectory, 0o666):
except OSError:
    sys.exit('Fatal: output directory "' + args.outputDirectory + '" does not exist and cannot be created')

If no OSError is thrown, that means the directory was successfully created.