How do I prevent Python's os.walk from walking across mount points?

Question

In Unix all disks are exposed as paths in the main filesystem, so os.walk('/') would traverse, for example, /media/cdrom as well as the primary hard disk, and that is undesirable for some applications.

How do I get an os.walk that stays on a single device?

Is there a way to determine if a subdirectory is in the same filesystem from python when using os.walk?

http://stackoverflow.com/questions/530645/is-there-a-way-to-determine-if-a-subdirectory-is-in-the-same-filesystem-from-pyth/530692#530692 — sykora, Feb 23 '09 at 14:44

Constantin · Accepted Answer · 2009-02-23T14:53:45.280

19

From os.walk docs:

When topdown is true, the caller can modify the dirnames list in-place (perhaps using del or slice assignment), and walk() will only recurse into the subdirectories whose names remain in dirnames; this can be used to prune the search

So something like this should work:

for root, dirnames, filenames in os.walk(...):
  dirnames[:] = [
    dir for dir in dirnames
    if not os.path.ismount(os.path.join(root, dir))]
  ...

edited Feb 23 '09 at 14:53

answered Feb 23 '09 at 14:39

Constantin

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a brilliantly concise answer. – Matt Joiner Oct 31 '09 at 01:57
As noted on the other comment: You can fool this with symlinks deeper into another filesystem. A better approach is to save the st_dev of the initial path (e.g. `dev0 = os.stat(startpath).st_dev`) and filter as `dirnames[:] = [d for d in dirnames if os.stat(os.path.join(root,d)).st_dev == dev0]` – Justin Winokur Mar 08 '22 at 14:29

score 3 · Answer 2 · edited May 23 '17 at 10:27

3

I think os.path.ismount might work for you. You code might look something like this:

import os
import os.path
for root, dirs, files in os.walk('/'):
    # Handle files.
    dirs[:] = filter(lambda dir: not os.path.ismount(os.path.join(root, dir)), 
                  dirs)

You may also find this answer helpful in building your solution.

*Thanks for the comments on filtering dirs correctly.

edited May 23 '17 at 10:27

Community

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answered Feb 23 '09 at 14:40

zweiterlinde

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You can fix is by chinging your code to "dirs[:] = filter(...)" instead, mutating the list in-place rather than reassiging – Brian Feb 23 '09 at 14:59
You can fool this with symlinks deeper into another filesystem. A better approach is to save the st_dev of the initial path (e.g. `dev0 = os.stat(startpath).st_dev`) and filter as `dirs[:] = [d for d in dirs if os.stat(os.path.join(root,d)).st_dev == dev0]` – Justin Winokur Mar 08 '22 at 14:28

score 1 · Answer 3 · edited Dec 03 '11 at 15:01

1

os.walk() can't tell (as far as I know) that it is browsing a different drive. You will need to check that yourself.

Try using os.stat(), or checking that the root variable from os.walk() is not /media

edited Dec 03 '11 at 15:01

Lesmana

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answered Feb 23 '09 at 14:31

Jason Coon

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How do I prevent Python's os.walk from walking across mount points?

3 Answers3

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