Python创建目录失败

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.

Answer 2

You don't need to call os.path.exists() (or os.path.isdir() ); os.makedirs() has exist_ok parameter.

And as @Thomas Orozco mentioned , you shouldn't check os.makedirs() ' return value because os.makedirs() indicates errors by raising an exception instead:

try:
    os.makedirs(args.output_dir, mode=0o666, exist_ok=True)
except OSError as e:
    sys.exit("Can't create {dir}: {err}".format(dir=output_dir, err=e))

Note: Unlike os.path.exist() -based solution; it raises an error if the path exists but it is not a directory (or a symlink to a directory).

There could be issues with the mode parameter, see the note for versions of Python before 3.4.1