[Python-Dev] My summary of the scandir (PEP 471) (original) (raw)

Jonas Wielicki j.wielicki at sotecware.net
Tue Jul 1 16:59:13 CEST 2014

On 01.07.2014 15:00, Ben Hoyt wrote:

I'm leaning towards preferring #2 (Nick's proposal) because it solves or gets around the caching issue. My one concern is error handling. Is it an issue if scandir's next can raise an OSError either from the readdir() call or the call to stat()? My thinking is probably not. In practice, would it ever really happen that readdir() would succeed but an os.stat() immediately after would fail? I guess it could if the file is deleted, but then if it were deleted a microsecond earlier the readdir() would fail anyway, or not? Or does readdir give you a consistent, "snap-shotted" view on things?

No need for a microsecond-timed deletion -- a directory with +r but without +x will allow you to list the entries, but stat calls on the files will fail with EPERM:

$ ls -l
drwxr--r--.   2 root     root        60  1. Jul 16:52 test

$ sudo ls -l test
total 0
-rw-r--r--. 1 root root 0  1. Jul 16:52 foo

$ ls test
ls: cannot access test/foo: Permission denied
total 0
-????????? ? ? ? ?             ? foo

$ stat test/foo
stat: cannot stat ‘test/foo’: Permission denied

I had the idea to treat a failing lstat() inside scandir() as if the entry wasn’t found at all, but in this context, this seems wrong too.

regards, jwi

More information about the Python-Dev mailing list