Here I think we need to drop our perfectionist attitude. When I saw
Marc-Andre's proposal my first response was also "but what about threads."
But really, os.chdir() is the culprit here, and since it's a syscall we
can't fix it. If we can live with that, we can live with the proposed
os.workdir(). The docs just need a warning about threads.
Yes, you could create a thread-safe version of this by overriding open() --
and several hundred other functions that refer to pathnames natively. Such
a project will inevitably have serious backwards compatibility concerns
(any use of pathnames from C extensions will not work right) so it's just
not going to be done.
If we don't offer this in the stdlib, users will just implement this
themselves, poorly (for example, by not restoring the original when done).
On Tue, Sep 14, 2021 at 2:43 PM Cameron Simpson <c...@cskk.id.au> wrote:
> On 14Sep2021 21:43, M.-A. Lemburg <m...@egenix.com> wrote:
> >- The context manager is not thread safe. There's no thread safe model
> > for the current work dir. OTOH, scripts usually don't use threads,
> > so not a big deal.
>
> This is the source of my concerns. Though of course it applies to any
> process global state. It would need this stated up front in big letters
> (as of course does chdir itself). My real concern is that this can leak
> into other functions whose use then makes whatever uses them to become
> inherently and unrepairably not thread safe.
>
> I know I'm atypical, but I have quite a lot of multithreaded stuff,
> including command line code. So while it'd be ok to avoid this context
> manager for my own code, I fear library modules, either stdlib or pypi,
> quietly using this in their code, making them unuseable in the general
> case. Unrepairably unuseable, for the user.
>
> I think what would be more useful is a context manager which worked on a
> threading.local which pushed/popped a reference directory path, and had
> an open() method which used that (and friends for other pathname based
> functions).
>
> In my own code I'd write this like (sketch, untested):
>
> from cs.threads import State as ThreadState
>
> class RefDir(ThreadState)
>
> def __init__(self, refpath=None):
> if refpath is None:
> refpath = os.getcwd()
> self.refpath = abspath(refpath)
>
> def open(self, path, *a, **kw):
> if not isabs(path):
> path = os.path.join(self.refpath, path)
> return open(path, *a, **kw) # calls the builtin open()
>
> ... listdir, mkdir, etc etc ...
>
> # on reflection, __enter__ and __exit__ would make the below even
> # more convenient
> @contextmanager
> def dirpath(newrefpath):
> ''' Push `newrefpath` for the duration of the context manager.
> '''
> with self(refpath=newrefpath):
> yield self.refpath
>
> and then use it like this:
>
> R = RefDir()
> ....
> with R.dirpath('/some/new/place') as newpath:
> ...
> with R.open("something.txt") as f:
> ... work on /some/new/place/something.txt ...
>
> In the above, cs.threads.State is a threading.lcoal subclass which is
> also a context manager whose operation pushes arbitrary attribute
> values. Great for thread safe execution scoped state. Like this
> example.
>
> All that said, I wrote pretty much exactly what you describe just the
> other week for umask().
>
> Cheers,
> Cameron Simpson <c...@cskk.id.au>
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--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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