[Python-Dev] Rationale for NamedTemporaryFile revisited [SEC=UNCLASSIFIED]

[Ole.Nielsen at ga.gov.au]

I found this posting, and those following it, as I too am baffled that
NamedTemporaryFile doesn't let you read the generated file - even within the
same script.
For unit testing it is very commonplace to generate a test file on the fly
and then use it as input the function being tested. NamedTemporaryFile would
be the perfect candidate for this except that the file seems to disappear
immediately after it has been closed. This is contrary to Dustin's comment
which states that the lifetime extends until the object is garbage collected.
The following script illustrates this isn't the case: 

from tempfile import NamedTemporaryFile
fid = NamedTemporaryFile(mode='w',
                         suffix='.tmp',
                         dir='.')
        
fid.write('My temp file')
fid.close()

# Read it (fid hasn't been garbage collected yet)
print fid.name

# But the file itself has gone
fid2 = open(fid.name)
print fid2.readlines()


Can someone please help point me to the best way of creating temporary files
in Python that can be read in immediately after their creation.

Thanks
Ole Nielsen, Geoscience Australia



On Sun, Mar 18, 2007 at 11:49:55AM +1200, Greg Ewing wrote:
> I've just discovered the hard way that NamedTemporaryFile
> automatically deletes the file when you close it. That
> doesn't seem very useful to me, since surely the reason
> you're using NamedTemporaryFile instead of TemporaryFile
> is that you want to do something else with it afterwards?
> What's the rationale for this behaviour?

For both TemporaryFile and NamedTemporaryFile, the rationale is that
"temporary" extends until the object is garbage collected.
TemporaryFile is deleted immediately (to prevent other applications from
modifying your temporary file).  NamedTemporaryFile is inteded for use
when you need access to the file by filename during the lifetime of the
file.  In either case, when the object goes, the file should too.

Dustin