How to check whether file is open or not

[Ros]

There are 10 files in the folder. I wish to process all the files one
by one. But if the files are open or some processing is going on them
then I do not want to disturb that process. In that case I would
ignore processing that particular file and move to next file.

How can I check whether the file is open or not?

I tried os.stat and os.access but I am not getting the expected
results.
Also I checked in IO exceptions, IO error handler doesnt raise any
error if the file is open.
There are some options to check but they are platform dependent (works
only with unix)

Your help would be highly appreciated.

Thanks,
Ros

 

[Diez B. Roggisch]

There are 10 files in the folder. I wish to process all the files one
by one. But if the files are open or some processing is going on them
then I do not want to disturb that process. In that case I would
ignore processing that particular file and move to next file.

How can I check whether the file is open or not?

I tried os.stat and os.access but I am not getting the expected
results.
Also I checked in IO exceptions, IO error handler doesnt raise any
error if the file is open.
There are some options to check but they are platform dependent (works
only with unix)

You can't do that, at least not in a platform agnostic way, and usually not
without cooperation of the file-modifying processes.

Diez

 

[Gabriel Genellina]

There are 10 files in the folder. I wish to process all the files one
by one. But if the files are open or some processing is going on them
then I do not want to disturb that process. In that case I would
ignore processing that particular file and move to next file.

How can I check whether the file is open or not?

I tried os.stat and os.access but I am not getting the expected
results.
Also I checked in IO exceptions, IO error handler doesnt raise any
error if the file is open.
There are some options to check but they are platform dependent (works
only with unix)

This works only on Windows:
You can use the _sopen function (from the C runtime library), which takes
additional flags for specifying file sharing. See
http://msdn2.microsoft.com/en-us/library/aa273350(VS.60).aspx
_sopen with _SH_DENYRW will fail if the file is already open by the same
or another process. Try to open the file using this flag: if _sopen
succeeds (does not return -1) the file was not already open (remember to
close it as soon as possible!); if _sopen fails (returns -1) it was
already open.

Using the ctypes module (included with Python 2.5; you can download and
install it for previous versions) you can call that function easily:

py> from ctypes import *
py> crt = cdll.msvcrt
py> _sopen = crt._sopen
py> _sopen.argtypes = (c_char_p, c_int, c_int, c_int)
py> _SH_DENYRW = 0x10 # from <share.h>
py> h = _sopen("C:\\1.txt", 0, _SH_DENYRW, 0)
py> h
3
py> h2 = _sopen("C:\\1.txt", 0, _SH_DENYRW, 0)
py> h2
-1
py> _close = crt._close
py> _close(h)
0
py> h2 = _sopen("C:\\1.txt", 0, _SH_DENYRW, 0)
py> h2
3
py> _close(h2)
0

Note: You said "But if the files are open or some processing is going on
them then I do not want to disturb that process.". There exist a (small)
risk of disturbing the other process: if it tries to open the file just
after you opened it, but before you close it, the operation will fail. It
is a tiny window, but might happen...

Surely there are other ways - some programs can report all processes
having a certain file opened, by example, but I don't know how to do that.

 

[Mattias Nilsson]

There are 10 files in the folder. I wish to process all the files one
by one. But if the files are open or some processing is going on them
then I do not want to disturb that process. In that case I would
ignore processing that particular file and move to next file.

How can I check whether the file is open or not?

<snip>

From what I know: You can't, in a platform independent way.

You'd still be in trouble even if python would let you write something like:

if file_is_open(filename):
process_file(filename)


There's nothing that says no one will open the file after the
file_is_open call but before the process_file call. Also, the file might
be opened during the processing.

If the files to be processed only are written and then closed without
being reopened or modified, then your situation is a bit simpler.

If you can get the process that creates the files to cooperate, a common
way to solve this problem is to have a temporary suffix on files while
they are being created. Once the file is complete, the temporary suffix
is removed and that signals to other processes that this file is ready
for processing.

 

[Ros]

Thanks a lot Gabriel.
ctypes is working!

Regards,
Ros

 

[Bart Ogryczak]

There are 10 files in the folder. I wish to process all the files one
by one. But if the files are open or some processing is going on them
then I do not want to disturb that process. In that case I would
ignore processing that particular file and move to next file.

If you can os.open() with O_EXLOCK flag, it's not open by other
process. Now that should work on Unix, Linux and MacOS X. All Windows
proceeding form NT line, are supposed to be POSIX compatible, but
somehow this flag is not available.

 

[Gabriel Genellina]

If you can os.open() with O_EXLOCK flag, it's not open by other
process. Now that should work on Unix, Linux and MacOS X. All Windows
proceeding form NT line, are supposed to be POSIX compatible, but
somehow this flag is not available.

O_EXLOCK is not in POSIX.