[Python-ideas] PEP 428 - joining

[Georg Brandl]

Am 07.10.2012 23:42, schrieb Antoine Pitrou:
> On Sun, 7 Oct 2012 23:15:38 +0200
> Yuval Greenfield <ubershmekel at gmail.com>
> wrote:
>> On Sun, Oct 7, 2012 at 7:37 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
>> 
>> > On Sat, 6 Oct 2012 10:44:37 -0700
>> > Guido van Rossum <guido at python.org> wrote:
>> > >
>> > > But rather than diving right into the syntax, I would like to focus on
>> > > some use cases. (Some of this may already be in the PEP, my
>> > > apologize.) Some things I care about (based on path manipulations I
>> > > remember I've written at some point or another):
>> > >
>> > > - Distinguishing absolute paths from relative paths; this affects
>> > > joining behavior as for os.path.join().
>> >
>> > The proposed API does function like os.path.join() in that respect:
>> > when joining a relative path to an absolute path, the relative path is
>> > simply discarded:
>> >
>> > >>> p = PurePath('a')
>> > >>> q = PurePath('/b')
>> > >>> p[q]
>> > PurePosixPath('/b')
>> >
>> >
>> What's the use case for this behavior?
>> 
>> I'd much rather if joining an absolute path to a relative one fail and
>> reveal the potential bug....
>> 
>>     >>> os.unlink(Path('myproj') / Path('/lib'))
>>     Traceback (most recent call last):
>>       File "<stdin>", line 1, in <module>
>>     TypeError: absolute path can't be appended to a relative path
> 
> In all honesty I followed os.path.join's behaviour here. I agree a
> ValueError (not TypeError) would be sensible too.

Please no -- this is a very important use case (for os.path.join, at least):
resolving a path from config/user/command line that can be given either absolute
or relative to a certain directory.

Right now it's as simple as join(default, path), and i'd prefer to keep this.
There is no bug here, it's working as designed.

Georg