[Python-Dev] When should pathlib stop being provisional?

Nick Coghlan ncoghlan at gmail.com
Wed Apr 6 02:57:49 EDT 2016

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.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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