[Python-Dev] Is adding support for os.PathLike an enhancement or bugfix?

[Koos Zevenhoven]

On May 5, 2017 10:39 PM, "Chris Barker" <chris.barker at noaa.gov> wrote:

Sorry to come late to the game, It wasn't immediately clear to me what the
implications were of the "enhancement or bugfix" distinction...

On Thu, May 4, 2017 at 9:46 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> That improved casting mechanism and the implicit support in the low
> level APIs is the main benefit I see in PEP 519, and if we were
> talking about an os module API that was missing os.path support, I'd
> be more likely to be on the "it's a bug" side of things.
>

absolutely.


> It's only higher level APIs like shutil that I put into the same
> category as third party libraries for now: Python 3.6 users shouldn't
> expect implicit use of the fspath protocol to be universal yet,


I think stdlib packages, like shutil are very much distinct from third
party  libs, and users certainly expect the entire stdlib to be updated to
support new language features.

We very often make the distinction between third party libs and stdlibs --
in fact, that is one reason we are reluctant to add new packages to the
stdlib...

Indeed, IIRC, that was the entire motivation for PEP 519 -- it started as a
"let's make Path objects work with the stdlib", but when we looked at how
to do that, it became clear that new protocol was teh best way to do that
and also provide flexibility to do that.

And the PEP states:

"""
Changes to Python's standard library are also proposed to utilize this
protocol where appropriate to facilitate the use of path objects where
historically only str and/or bytes file system paths are accepted. The goal
is to facilitate the migration of users towards rich path objects while
providing an easy way to work with code expecting str or bytes .
"""

It doesn't actually say "everywhere possible in the stdlib", but if the
goal is to facilitate migration, as stated, then the any but truly obscure
functions should be covered -- and shutil is certainly not obscure.


Indeed.

So it would be really great if any updates to shutils (and other stdlib
packages) to support the new protocol be back-ported.

Yes, it's "just" adding an extra call, but in my experience, low barrier to
entry are enough to discourage adoption -- and handful of shutil function
failing will certainly be enough to keep some folks from adopting the new
approach.


I suppose the worst thing to happen is what Eric describes. But technically
speaking, passing os.PathLike to shutil functions might currently be
undefined behavior, so the change is 'legal' if it's not documented ;).

-- Koos (mobile)
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