tempfile.NamedTemporaryFile wont work

[Peter Otten]

Steven D'Aprano wrote:

> On Sun, 19 Nov 2006 13:11:13 +0100, Imbaud Pierre wrote:
> 
>> On suse 9.3, tempfile.NamedTemporaryFile() doesnt work as expected.
> [snip]
> 
>> Symptom: the file does not always exist, after the call to
>> NamedTemporaryFile(). Or at least its not seen by the strings command,
>> or by os.path.exists.
>> 
>> I guess the bug is pretty much os dependent, or even filesystem
>> dependent (Im on reiserfs). Maybe the os is buggy, maybe, somehow, the
>> python interface. Or did I miss something?
>> Shame, I didnt even try to check for a python bug tracker.
> 
> I can verify this problem occurs on Fedora Core 5 too:
> 
> import os
> import sys
> import tempfile
> import subprocess
> def test(n):
> chunk = ': +++ abcd +++'
> for i in xrange(n):
> tf = tempfile.NamedTemporaryFile()
> tfName = tf.name
> tf.seek(0)
> tf.write(str(i) + chunk)
>                 tf.flush()
> if not os.path.exists(tfName):
> print 'pre-check: %s not there' % tfName
> subprocess.Popen(['strings', tfName])
> if not os.path.exists(tfName):
> print 'post-check: %s not there' % tfName
> 
> 
> And here is a typical run, with the boring bits removed for ease of
> reading:
> 
>>>> test(30)
> 0: +++ abcd +++
> 1: +++ abcd +++
>     [ more of the same ]
> 14: +++ abcd +++
> strings: '/tmp/tmpOALbx9': No such file
> 16: +++ abcd +++
> 17: +++ abcd +++
> 18: +++ abcd +++
>     [ more of the same ]
> 27: +++ abcd +++
> strings: /tmp/tmpdc52Nz: No such file or directory
> 29: +++ abcd +++
> 
> 
> Curiouser and curiouser... not only does os.path.exist always report the
> temp file as existing (at least in my tests), even when strings can't find
> it, but strings returns different error messages.
> 
> Is it possible this is a bug in strings?

What /you/ are seeing is not a bug, I think. Popen() is asynchronous,
therefore you may enter the second iteration -- which implicitly closes the
temporary file -- before strings actually tries to access it. Use call()
and everything should be fine.

Peter