[Python-Dev] PEP 428: Pathlib -> stat caching

[Brett Cannon]

On Mon, Sep 16, 2013 at 3:45 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Mon, 16 Sep 2013 19:06:37 +0200
> Charles-François Natali <cf.natali at gmail.com> wrote:
> > 2013/9/16 Antoine Pitrou <solipsis at pitrou.net>:
> > > Le Sun, 15 Sep 2013 06:46:08 -0700,
> > > Ethan Furman <ethan at stoneleaf.us> a écrit :
> > >> I see PEP 428 is both targeted at 3.4 and still in draft status.
> > >>
> > >> What remains to be done to ask for pronouncement?
> > >
> > > I think I have a couple of items left to integrate in the PEP.
> > > Mostly it needs me to take a bit of time and finalize the PEP, and
> > > then have a PEP delegate (or Guido) pronounce on it.
> >
> > IIRC, during the last discussion round, we were still debating between
> > implicit stat() result caching - which requires an explicit restat()
> > method - vs a mapping between the stat() method and a stat() syscall.
> >
> > What was the conclusion?
>
> No definite conclusion. You and Nick liked the idea of a rich stat
> object (returned by os.stat()) with is_dir() methods and the like:
> https://mail.python.org/pipermail/python-dev/2013-May/125809.html
>
> However, nothing was done about that since then ;-)
>
> There was also the scandir() proposal to return rich objects with
> optional stat-like fields, but similarly it didn't get a conclusion:
> https://mail.python.org/pipermail/python-dev/2013-May/126119.html
>
> So I would like to propose the following API change:
>
> - Path.stat() (and stat-accessing methods such as get_mtime()...)
>   returns an uncached stat object by default
>
> - Path.cache_stat() can be called to return the stat() *and* cache it
>   for future use, such that any future call to stat(), cache_stat() or
>   a stat-accessing function reuses that cached stat
>
> In other words, only if you use cache_stat() at least once is the
> stat() value cached and reused by the Path object.
> (also, it's a per-Path decision)
>

Any reason why stat() can't get a keyword-only cached=True argument
instead? Or have stat() never cache() but stat_cache() always so that
people can choose if they want fresh or cached based on API and not whether
some library happened to make a decision for them?
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