[Tutor] Request for help with os.walk() combining os.path.ismount() in Linux

Srihari Vijayaraghavan linux.bug.reporting at gmail.com
Thu Aug 20 10:51:02 CEST 2015

On 20 August 2015 at 18:25, Alan Gauld <alan.gauld at btinternet.com> wrote:
> On 20/08/15 04:03, Srihari Vijayaraghavan wrote:
>> out = sys.stdout.write
>> for root, dirs, files in os.walk("/"):
>>     out("The dirs before removing mount points: %s\n" % dirs)
>>     for d in dirs:
>>         dname = os.path.join(root, d)
>>         if os.path.ismount(dname):
>>             dirs.remove(d)
> It's never a good idea to remove items from the thing
> you are iterating over. Create a copy of dirs (dirs[:])
> to iterate on then remove the items from the original
> dirs.

In general I agree, but this is what the os.walk() document states:
"... When topdown is True, the caller can modify the dirnames list
in-place (perhaps using del or slice assignment)..."

(Yes, the topdown argument of os.walk() is True by default, until
manually modified.)

Therefore I see no problem with in-place modification of dirnames.
I've made a copy of dirs & iterated over it, which made no difference
in my case.

My issue is that some of the virtual or in memory file systems' mount
points (like /proc, /dev) are failing to be recognised properly under
os.path.ismount(). Perhaps this quirkiness is irresolvable??

Thank you.

Srihari Vijayaraghavan

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