[Python-Dev] Adding test.support.safe_rmpath()

Giampaolo Rodola' g.rodola at gmail.com
Thu Feb 14 10:24:41 EST 2019

On Thu, Feb 14, 2019 at 4:03 PM Tim Golden <mail at timgolden.me.uk> wrote:

> On 14/02/2019 14:56, Giampaolo Rodola' wrote:
> >
> >
> > On Thu, Feb 14, 2019 at 3:25 PM Eric Snow <ericsnowcurrently at gmail.com
> > <mailto:ericsnowcurrently at gmail.com>> wrote:
> >
> >     On Thu, Feb 14, 2019, 02:47 Ronald Oussoren via Python-Dev
> >     <python-dev at python.org <mailto:python-dev at python.org> wrote:
> >
> >
> >         I usually use shutil.rmtree for tests that need to create
> >         temporary files, and create a temporary directory for those
> >         files (that is, use tempfile.mkdtemp in setUp() and use
> >         shutil.rmtree in tearDown()). That way I don’t have to adjust
> >         house-keeping code when I make changes to test code.
> >
> >
> >     Same here.
> >
> >     -eric
> >
> >
> > What I generally do is avoid relying on tempfile.mkdtemp() and always
> > use TESTFN instead. I think it's cleaner as a pradigm because it's an
> > incentive to not pollute the single unit tests with  `self.addCleanup()`
> > instructions (the whole cleanup logic is always supposed to occur in
> > setUp/tearDown):
> Must chime in here because I've been pushing (variously months & years
> ago) to move *away* from TESTFN because it generates numerous
> intermittent errors on my Windows setup. I've had several goes at
> starting to do that but a combination of my own lack of time plus some
> people's reluctance to go that route altogether has stalled the thing.
> I'm not sure I understand the difference in cleanup/teardown terms
> between using tempfile and using TESTFN. The objections I've seen from
> people (apart, obviously, from test churn) are to do with building up
> testing temp artefacts on a possibly low-sized disk.

I suppose you mean the intermittent failures are usually due to "file is
already in use by another process" correct? test.support's unlink(),
rmdir() and rmtree() functions already implement a retry-with-timeout logic
in order to prevent this issue. I suppose when this issue may still occur,
though, is when the file/handle is held by another process, meaning that
the unit-test probably forgot to terminate()/wait() a subprocess or should
have used support.read_children(). In summary, my approach is more "strict"
because it implies that unit-tests always do a proper cleanup.
tempfile.mkdtemp() may prevent failures but it may hide a unit-test which
doesn't do a proper file/dir cleanup and should have been fixed instead.
The drawback in practical terms is that orphaned test files are left behind.

Extra: an argument in favor of using tempfile.mkdtemp() instead of TESTFN
is parallel testing, but I think we're not using it.

Giampaolo - http://grodola.blogspot.com
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