[Python-Dev] file system path protocol PEP

[Brett Cannon]

On Wed, 11 May 2016 at 13:45 Serhiy Storchaka <storchaka at gmail.com> wrote:

> On 11.05.16 19:43, Brett Cannon wrote:
> > os.path
> > '''''''
> >
> > The various path-manipulation functions of ``os.path`` [#os-path]_
> > will be updated to accept path objects. For polymorphic functions that
> > accept both bytes and strings, they will be updated to simply use
> > code very much similar to
> > ``path.__fspath__() if  hasattr(path, '__fspath__') else path``. This
> > will allow for their pre-existing type-checking code to continue to
> > function.
>
> I afraid that this will hit a performance. Some os.path functions are
> used in tight loops, they are hard optimized, and adding support of path
> protocol can have visible negative effect.
>

As others have asked, what specific examples do you have that os.path is
used in a tight loop w/o any I/O that would overwhelm the performance?


>
> I suggest first implement other changes and then look whether it is
> worth to add support of path protocol in os.path functions.
>

I see this whole discussion breaking down into a few groups which changes
what gets done upfront and what might be done farther down the line:

   1. Maximum acceptance: do whatever we can to make all representation of
   paths just work, which means making all places working with a path in the
   stdlib accept path objects, str, and bytes.
   2. Safely use path objects: __fspath__() is there to signal an object is
   a file system path and to get back a lower-level representation so people
   stop calling str() on everything, providing some interface signaling that
   someone doesn't misuse an object as a path and only changing path
   consumptions APIs -- e.g. open() -- and not path manipulation APIs -- e.g.
   os.path -- in the stdlib.
   3. It ain't worth it: those that would rather just skip all of this and
   drop pathlib from the stdlib.

Ethan and Koos are in group #1 and I'm personally in group #2 but I tried
to compromise somewhat and find a middle ground in the PEP with the level
of changes in the stdlib but being more restrictive with os.fspath(). If I
were doing a pure group #2 PEP I would drop os.path changes and make
os.fspath() do what Ethan and Koos have suggested and simply pass through
without checks whatever path.__fspath__() returned if the argument wasn't
str or bytes.
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