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

Antoine Pitrou solipsis at pitrou.net
Mon Sep 16 22:05:46 CEST 2013

On Mon, 16 Sep 2013 15:48:54 -0400
Brett Cannon <brett at python.org> wrote:
> >
> > 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?

1. Because you also want the helper functions (get_mtime(), etc.) to
cache the value too. It's not only about stat().

2. Because of the reverse use case where you want a library to reuse a
cached value despite the library not using an explicit caching call.

Basically, the rationale is:

1. Caching should be opt-in, which is what this new API achieves.

2. Once you have asked for caching, most always you also want the
subsequent accesses to be cached.

I realize there should be a third method clear_cache(), though ;-)



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