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

Paul Moore p.f.moore at gmail.com
Thu Jan 26 14:15:08 CET 2006

On 1/25/06, BJörn Lindqvist <bjourne at gmail.com> wrote:

My comments on the issues. It was easier this way than trying to reply on every message individually.

Inheritance from string (Jason) This issue has been brought up before when people were discussing the path module. I think the consensus is that, while the inheritance isn't pure, practicality beats purity. It would require to big changes to Python and would break to much existing code to not extend string. I'll add this to Resolved Issues if nobody minds.

I mind (see my previous post)...

Remove div (Ian, Jason, Michael, Oleg)

This is one of those where everyone (me too) says "I don't care either way." If that is so, then I see no reason to change it unless someone can show a scenario in which it hurts readability. Plus, a few people have said that they like the shortcut.

Hardly. I've seen some pretty strong arguments (both for and against)

FWIW, I find the / operator ugly. Also, multiple concatenation (path / "a" / "b" / "c") results in building lots of intermediates, where path.join("a", "b", "c") need not. Arguing that you can't reuse string methods is bogus, IMHO, as the requirement to subclass from string is far from clear.

Actually, reading that, I'd suggest:

So, we have

Quick question - how do Path objects constructed from relative paths behave? Are there such things as relative path objects? Consider

p1 = Path("a")
p2 = Path("b")

Is p1.append(p2) (or p1/p2) legal? What does it mean? I'd have to assume it's the same as Path("a", "b"), but I'm not sure I like that... What about Path("/a").append(Path("/b")) ???

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?

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'

But os.path manipulates strings representing pathnames (and I can forgive oddities like this by noting that some rules about pathnames are pretty subtle...). I'd have higher standards for a dedicated Path object.

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

str(Path("whatever")) === os.path.abspath("whatever")

It also allows Path("C:", "Windows") to do different things on Windows and Unix (absolute on Windows, relative to os.curdir on Unix).

This would imply that Path("a", a_path) or a_path.append(another_path) is an error. And of course, for this to work, Path objects can't be a subclass of string... :-)

Paul.

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