[Python-Dev] Defining a path protocol (was: When should pathlib stop being provisional?)

[Brett Cannon]

On Wed, 6 Apr 2016 at 12:29 Ryan Gonzalez <rymg19 at gmail.com> wrote:

> --
> Ryan
> [ERROR]: Your autotools build scripts are 200 lines longer than your
> program. Something’s wrong.
> http://kirbyfan64.github.io/
>
>
> On Apr 6, 2016 12:28 PM, "Brett Cannon" <brett at python.org> wrote:
> >
> > WIth Ethan volunteering to do the work to help make a path protocol a
> thing -- and I'm willing to help along with propagating this through the
> stdlib where I think Serhiy might be interested in helping as well -- and a
> seeming consensus this is a good idea, it seems like this proposal has a
> chance of actually coming to fruition.
> >
> > Now we need clear details. :) Some open questions are:
>
> My votes:
>
> > Name: __path__, __fspath__, or something else?
>
> __path__. Considering everything related to `pathlib` uses the word
> `path`, __fspath__ seems kind of odd.
>
> > Method or attribute? (changes what kind of one-liner you might use in
> libraries, but I think historically all protocols have been methods and the
> serialized string representation might be costly to build)
>
> Method. Using an attribute would be needlessly inconsistent.
>
> > Built-in? (name is dependent on #1 if we add one)
> > Add the method/attribute to str? (I assume so, much like __index__() is
> on int, but I have not seen it explicitly stated so I would rather clarify
> it)
>
> I agree; this would avoid lots of excess complexity.
>
> > Expand the C API to have something like PyObject_Path()?
>
> -1. PyFileObject was already removed from Python 3; it seems useless to
> add another one.
>

But that was removing a custom object, not a function that will implement
whatever idiom we come up with for getting the string representation of a
path.

-Brett


> >
> > Some people have asked for the pathlib PEP to have a more flushed out
> reasoning as to why pathlib doesn't inherit from str. If Antoine doesn't
> want to do it I can try to instil my blog post into a more succinct
> paragraph or two and update the PEP myself.
> >
> > Is this going to require a PEP or if we can agree on the points here are
> we just going to do it? If we think it requires a PEP I'm willing to write
> it, but I obviously have no issue if we skip that step either. :)
> >
> > Oh, and we should resolve this before the next release of Python 3.4,
> 3.5, or 3.6 so that pathlib can be updated in those releases.
> >
> > -Brett
> >
> >
> > On Wed, 6 Apr 2016 at 08:09 Ethan Furman <ethan at stoneleaf.us> wrote:
> >>
> >> On 04/05/2016 11:57 PM, Nick Coghlan wrote:
> >> > On 6 April 2016 at 16:53, Nathaniel Smith <njs at pobox.com> wrote:
> >> >> On Tue, Apr 5, 2016 at 11:29 PM, Nick Coghlan <ncoghlan at gmail.com>
> wrote:
> >>
> >> >>> I'd missed the existing precedent in DirEntry.path, so simply taking
> >> >>> that and running with it sounds good to me.
> >> >>
> >> >> This makes me twitch slightly, because NumPy has had a whole set of
> >> >> problems due to the ancient and minimally-considered decision to
> >> >> assume a bunch of ad hoc non-namespaced method names fulfilled some
> >> >> protocol -- like all .sum methods will have a signature that's
> >> >> compatible with numpy's, and if an object has a .log method then
> >> >> surely that computes the logarithm (what else in computing could
> "log"
> >> >> possibly refer to?), etc. This experience may or may not be relevant,
> >> >> I'm not sure -- sometimes these kinds of twitches are good guides to
> >> >> intuition, and sometimes they are just knee-jerk responses to an old
> >> >> and irrelevant problem :-)
> >> >>
> >> >> But you might want to at least think about
> >> >> how common it might be to have existing objects with unrelated
> >> >> attributes that happen to be called "path", and the bizarro problems
> >> >> that might be caused if someone accidentally passes one of them to a
> >> >> function that expects all .path attributes to be instances of this
> new
> >> >> protocol.
> >> >
> >> > sys.path, for example.
> >> >
> >> > That's why I'd actually prefer the implicit conversion protocol to be
> >> > the more explicitly named "__fspath__", with suitable "__fspath__ =
> >> > path" assignments added to DirEntry and pathlib. However, I'm also not
> >> > offering to actually *do* the work here, and the casting vote goes to
> >> > the folks pursuing the implementation effort.
> >>
> >> If we decide upon __fspath__ (or __path__) I will do the work on pathlib
> >> and scandir to add those attributes.
> >
> >
>
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