[Python-Dev] Defining a path protocol

Michel Desmoulin desmoulinmichel at gmail.com
Wed Apr 6 13:35:25 EDT 2016

Wouldn't be better to generalize that to a "__location__" protocol,
which allow to return any kind of location, including path, url or
coordinate, ip_address, etc ?

Le 06/04/2016 19:26, Brett Cannon a écrit :
> 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:
>  1. Name: __path__, __fspath__, or something else?
>  2. 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)
>  3. Built-in? (name is dependent on #1 if we add one)
>  4. 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)
>  5. Expand the C API to have something like PyObject_Path()?
> 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
> <mailto: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
>     <mailto:njs at pobox.com>> wrote:
>     >> On Tue, Apr 5, 2016 at 11:29 PM, Nick Coghlan <ncoghlan at gmail.com
>     <mailto: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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