[Python-Dev] PEP 3147, __pycache__ directories and umask

[Brett Cannon]

On Mon, Mar 22, 2010 at 06:56, Barry Warsaw <barry at python.org> wrote:
> I have a pretty good start on PEP 3147 implementation [1], but I've
> encountered a situation that I'd like to get some feedback on.  Here's the
> test case illustrating the problem.  From test_import.py:
>
>    def test_writable_directory(self):
>        # The umask is not conducive to creating a writable __pycache__
>        # directory.
>        with umask(0o222):
>            __import__(TESTFN)
>        self.assertTrue(os.path.exists('__pycache__'))
>        self.assertTrue(os.path.exists(os.path.join(
>            '__pycache__', '{}.{}.pyc'.format(TESTFN, self.tag))))
>
> The __pycache__ directory does not exist before the import, and the import
> machinery creates the directory, but the umask leaves the directory unwritable
> by anybody.  So of course when the import machinery goes to write the .pyc
> file inside __pycache__, it fails.  This does not cause an ImportError though,
> just like if today the package directory were unwritable.
>
> This might be different than today's situation though because once the
> unwritable __pycache__ directory is created, nothing is going to change that
> without explicit user interaction, and that might be difficult after the
> fact.
>
> I'm not sure what the right answer is.  Some possible choices:
>
> * Tough luck
> * Force the umask so that the directory is writable, but then the question is,
>  by whom?  ugo+w or something less?
> * Copy the permissions from the parent directory and ignore umask
> * Raise an exception or refuse to create __pycache__ if it's not writable
>  (again, by whom?)

I say tough luck. At the moment if you can't write a .pyc it is a
silent failure; don't see the difference as significant enough to
warrant changing the practice.

-Brett

>
> Or maybe you have a better idea?  What's the equivalent situation on Windows
> and how would things work there?
>
> -Barry
>
> [1] https://edge.launchpad.net/~barry/python/pep3147
>
> P.S. I'm down to only 8 unit test failures.
>
>
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