[Python-Dev] test___all__ polluting sys.modules?

[Gregory P. Smith]

On Sun, Dec 30, 2012 at 6:48 AM, R. David Murray <rdmurray at bitdance.com>wrote:

> On Mon, 31 Dec 2012 00:38:47 +1000, Nick Coghlan <ncoghlan at gmail.com>
> wrote:
> > On Mon, Dec 31, 2012 at 12:19 AM, Eli Bendersky <eliben at gmail.com>
> wrote:
> > > On Sun, Dec 30, 2012 at 5:54 AM, Stefan Krah <stefan at bytereef.org>
> wrote:
> > >>
> > >> Eli Bendersky <eliben at gmail.com> wrote:
> > >> > Yes, this is the solution currently used in test_xml_etree. However,
> > >> > once
> > >> > pickling tests are added things stop working. Pickle uses
> __import__ to
> > >> > import
> > >> > the module a class belongs to, bypassing all such trickery. So if
> > >> > test___all__
> > >> > got _elementtree into sys.modules, pickle's __import__ finds it
> even if
> > >> > all the
> > >> > tests in test_xml_etree manage to ignore it for the Python version
> > >> > because they
> > >> > use import_fresh_module.
> > >>
> > >> I ran into the same problem for test_decimal. The only thing that
> appears
> > >> to work is to set sys.modules['decimal'] explicitly before calling
> > >> dumps()/loads(). See:
> > >>
> > >>    PythonAPItests.test_pickle()
> > >>    ContextAPItests.test_pickle()
> > >
> > > Yes, this seems to have done the trick. Thanks for the suggestion.
> >
> > It may be worth offering a context manager/decorator equivalent to
> > "import_fresh_module".
>
> I suggested making import_fresh_module a context manager in the issue
> that Eli opened about test___all__.
>
> > > I'm still curious about the test-in-clean-env question though.
> >
> > As Stefan noted, the main advantage we get is that sometimes the
> > failure to clean up properly is in the standard lib code rather than
> > the tests, and with complete isolation we'd be less likely to notice
> > the problem.
> >
> > Once you combine that with the fact that rearchitecting regrtest to
> > work that way would be quite a bit of work, the motivation to make it
> > happen goes way down.
> >
> > However, specifically spinning out the "import the world" tests like
> > test_pydoc and test___all__ to a separate process might be worth the
> > effort.
>
> Adding something to regertest (or unittest?) so that certain nominated
> test modules are run in a subprocess has been discussed previously, but
> so far no one has stepped up to implement it :)  (I think this came up
> originally for test_site, but I don't remember for sure.)
>

test_subprocess and possibly a few others (things testing signal behavior,
etc) already have some individual tests that do this.  its pretty easy.
 subprocess.Popen of sys.executable typically with -E and the code either
in a string via -c or else point at a second file or add an argument for
main in the current file to detect.  making this simpler via something in
test.support might make sense if there is a common need for it.

-gps
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