[Python-Dev] os.path.normcase rationale? (original) (raw)

Chris Withers chris at simplistix.co.uk
Fri Oct 8 10:41:50 CEST 2010

On 05/10/2010 12:04, Steven D'Aprano wrote:

On Tue, 5 Oct 2010 07:21:15 pm Chris Withers wrote:

On 25/09/2010 04:25, Steven D'Aprano wrote:

1. Return the case of a filename in some canonical form which depends on the file system? 2. Return the case of a filename as it is actually stored on disk?

How do 1 and 2 differ? Case #1 imposes a particular canonical form, regardless of what is actually stored on disk. It is similar to normpath, except that we could have different canonical forms depending on what the file system was. normpath merely generalises from the operating system, and never looks at the file system.

Ah, okay, yeah, that's actually an anti-goal for me ;-)

Case #2 says to actually look at the file and see what the file system considers it's name to be. Consider a NTFS file system. By default it is case-preserving and case-insensitive, although that can be changed. (Just because a file system is NTFS doesn't mean that will be case-insensitive. NTFS can also run in a POSIX mode which is case-sensitive. But I digress.)

Yeah, this is definitely where I think the missing use case lies...

FWIW, the use case that setuptools has (and for which it currently incorrectly uses normpath) is number 2.

4. Return the case of a filename in some arbitrarily-chosen canonical form which does not depend on the file system? This is what normpath does, but only if you're on Windows ;-) Not quite. macpath.normcase() also lowercases the path. So does the module for OS/2.

Interesting, since I develop on MacOS, Linux and Windows and only experienced the problem caused by setuptools normcase'ing distribution names on Windows. The MacOS case also isn't in the docs.

In any case, Windows is not a file system. It is quite possible to have virtually any combination of case-destroying, case-preserving, -sensitive and -insensitive file systems on the one Windows system. Say, a FAT12 floppy, an NTFS partition, and an ext2 USB stick. Windows doesn't ship with native support for ext2, but that doesn't mean it can't be installed with third party drivers.

yes, exactly!

normpath pays no attention to any of this, and just lowercases the path. At least that's cheap, and consistent, even if it solves the wrong problem :)

...and creates a few more along the way ;-)

Chris

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