How to determine that if a folder is empty?

[could ildg]

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?
Thanks~

[Neil Hodgson]

could ildg:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

The first thing to do is measure the performance of this operation
in the context of your application to see if it is really worth extra
effort.
Tweaking this will depend on the platform. On Windows you can use
ctypes and the system functions FindFirstFile/FindNextFile/FindClose,
finishing once you see a single file. Directories always contain "." and
".." entries so they should be ignored. On other platforms there will be
similar low level functions.

Neil

[could ildg]

Thank you .
so you mean that this is not platform-independent?

On 8/8/05, Neil Hodgson <ny************ *****@gmail.com > wrote:

could ildg:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

The first thing to do is measure the performance of this operation
in the context of your application to see if it is really worth extra
effort.
Tweaking this will depend on the platform. On Windows you can use
ctypes and the system functions FindFirstFile/FindNextFile/FindClose,
finishing once you see a single file. Directories always contain "." and
".." entries so they should be ignored. On other platforms there will be
similar low level functions.

Neil
--
http://mail.python.org/mailman/listinfo/python-list

[Reinhold Birkenfeld]

could ildg wrote:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

try:
os.rmdir(path)
empty = True
except OSError:
empty = False

should be efficient. A directory (please stop calling them "folders")
can only be removed if it's empty.

Reinhold

[James Dennett]

Reinhold Birkenfeld wrote:

could ildg wrote:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

try:
os.rmdir(path)
empty = True
except OSError:
empty = False

should be efficient. A directory (please stop calling them "folders")
can only be removed if it's empty.

Reinhold

Unfortunately that destroys the directory if it was empty,
and then you can't recreate it unless (a) you went to the
trouble of preserving all of its attributes before deleting
it, and (b) your script has OS-level permissions to recreate
the directory with its original attributes (such as owners
and permissions).

Also note that modifying a filesystem can be significantly
slower than reading from it (it varies widely across platforms).

-- James

[Neil Hodgson]

could ildg

so you mean that this is not platform-independent?

Your existing code is platform-independent but I think for faster
code you will need to write platform-dependent code. FindFirstFile is
only available on Windows.

Neil

[John Machin]

Reinhold Birkenfeld wrote:

could ildg wrote:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

try:
os.rmdir(path)
empty = True
except OSError:
empty = False

should be efficient.

But it removes the folder if it is empty. Perhaps it's not efficient to
create the folder again.

[Peter Hansen]

could ildg wrote:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

I'm just curious to know under what circumstances where it's important
to know whether a directory is empty it's also important that the
operation occur with lightning speed...

Reinhold's suggestion to delete the folder was interesting in this
respect... isn't that (prior to deleting a folder) just about the only
time one cares if it's empty, normally? And in this case you don't need
to do the check, as Reinhard shows, so performance isn't an issue.

-Peter

[Mike Meyer]

James Dennett <jd******@acm.o rg> writes:

Reinhold Birkenfeld wrote:

could ildg wrote:

I want to check if a folder named "foldername " is empty.
I use os.listdir(fold ername)==[] to do this,
but it will be very slow if the folder has a lot of sub-files.
Is there any efficient ways to do this?

try:
os.rmdir(path)
empty = True
except OSError:
empty = False
should be efficient. A directory (please stop calling them "folders")
can only be removed if it's empty.
Reinhold

Unfortunately that destroys the directory if it was empty,
and then you can't recreate it unless (a) you went to the
trouble of preserving all of its attributes before deleting
it, and (b) your script has OS-level permissions to recreate
the directory with its original attributes (such as owners
and permissions).

It's also buggy, in that there are other things that can cause an
OSError:

import os
os.rmdir("/tmp/x") Traceback (most recent call last):
File "<stdin>", line 1, in ?
OSError: [Errno 1] Operation not permitted: '/tmp/x' ^D

bhuda% bhuda% ls -a /tmp/x
.. ..

The problem here is that I don't own /tmp/x, so I can't delete it,
hence I get an OSError even though it's empty.

Just out of curiosity, is there an OS out there where you can have the
permissions needed to delete a directory without having the
permissions needed to create it appropriately?

<mike
--
Mike Meyer <mw*@mired.or g> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

[Dan Sommers]

On Mon, 08 Aug 2005 09:03:39 -0400,
Mike Meyer <mw*@mired.or g> wrote:

Just out of curiosity, is there an OS out there where you can have the
permissions needed to delete a directory without having the
permissions needed to create it appropriately?

Depending on your definition of "out there," yes, some OS's grant those
privileges separately. Apollo (eventually bought out by HP) Aegis
(mostly like *nix, but just different enough to trip me up again and
again) used to be one. The more secure the environment, the more likely
certain privileges do *not* imply others.

Regards,
Dan

--
Dan Sommers
<http://www.tombstoneze ro.net/dan/>