[Python-Dev] The path module PEP (original) (raw)

Paul Moore p.f.moore at gmail.com
Fri Jan 27 11:16:09 CET 2006

On 1/26/06, Stefan Rank <stefan.rank at ofai.at> wrote:

on 26.01.2006 14:15 Paul Moore said the following: [snip] > > Also note that my example Path("C:", "Windows", "System32") above is > an absolute path on Windows. But a relative (albeit stupidly-named > :-)) path on Unix. How would that be handled?

wrong, Path("C:", "Windows", "System32") is a relative path on windows. see below.

Hmm, relative to the CWD on C: is a valid concept, and that is a potential meaning. I hadn't thought of that.

> Not that os.path gets it perfect: > > Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on win32 > Type "help", "copyright", "credits" or "license" for more information. >>>> import os >>>> os.path.join("C:", "Windows", "System32") > 'C:Windows\System32' >>>> os.path.join(".", os.path.join("C:", "Windows", "System32")) > '.\C:Windows\System32' >

this is misleading. observe:: In [1]: import os In [2]: os.path.join(".", os.path.join("C:", "Windows", "System32")) Out[2]: '.\C:Windows\System32' but:: In [3]: os.path.join(".", os.path.join("C:\", "Windows", "System32")) Out[3]: 'C:\Windows\System32'

The second example uses an absolute path as second argument, and as os.path.join should do, the first argument is discarded. The first case is arguably a bug, since, on windows, C:Windows\System32 is a path relative to the current directory on disk C: If the cwd on C: would be C:\temp then C:Windows\System32 would point to C:\temp\Windows\System32 The problem is that Windows has a cwd per partition... (I cannot even guess why ;-)

Thanks for the clarification, you are right in your analysis. However, it doesn't really affect my main point, which was that there should be no such thing as a relative Path (please note - I say "Path" here, to refer to the new Path object, as opposed to the general concept of an OS file path).

[...]

> Arguably, Path objects should always maintain an absolute path - there > should be no such thing as a relative Path. So you would have

you realise that one might need and/or want to represent a relative path?

Absolutely. But not a Path (see distinction above).

Aaron Bingham's analogy with time/timedelta applies well here. Relative paths, like relative times, have their own special semantics, which deserve to be addressed in a separate class.

You argue that time is "merely" a timedelta with a fixed start point. I'd disagree - the key point with timedeltas is that they need careful handling (DST issues, for example) depending upon precisely what they are added to - these issues are avoided by the time type exactly because it has a constant base. In exactly the same way, absolute paths have simpler semantics precisely because they are absolute.

Paul.

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