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

Brett Cannon brett at python.org
Wed Apr 6 13:26:36 EDT 2016

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> 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. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160406/ce4f4985/attachment.html>

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