Cameron Laird wrote:

In article <mailman.982310784.27748.python-list@python.org>, Tim Peters <tim.one@home.com> wrote:

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[Michael Hudson]

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... * Imports on case-insensitive file systems *

There was quite some discussion about how to handle imports on a case-insensitive file system (eg. on Windows). I didn't follow the details, but Tim Peters is on the case (sorry), so I'm confident it will get sorted out.

You can be sure the whitespace will be consistent, anyway <wink>. . . . them is ugly. We're already supporting (and will continue to support) PYTHONCASEOK for their benefit, but they don't deserve multiple hacks in 2001.

Flame at will.

or-flame-at-tim-your-choice-ly y'rs - tim

1. Thanks. Along with all the other benefits, I find this explanation FAR more entertaining than anything network television broadcasts (although nearly as tendentious as "The West Wing"). 2. I hope a few OS/400 and OpenVMS refugees convert and walk through the door soon. *That* would make for a nice dose of fun.

Let's see if I can explain the OpenVMS part. I'll do so by walking over Tim's text. (I'll step carefully over it. I don't intend to destroy it, Tim ;-) ] Here's the scoop: file systems vary across platforms in whether or not they ] preserve the case of filenames, and in whether or not the platform C library ] file-opening functions do or don't insist on case-sensitive matches: ] ] ] case-preserving case-destroying ] +-------------------+------------------+ ] case-sensitive | most Unix flavors | brrrrrrrrrr | ] +-------------------+------------------+ ] case-insensitive | Windows | some unfortunate | ] | MacOSX HFS+ | network schemes | ] | Cygwin | | | | OpenVMS | ] +-------------------+------------------+ Phew. I'm glad we're only 'unfortunate' and not in the 'brrrrrrrrrr' section ;-) ] In the upper left box, if you create "fiLe" it's stored as "fiLe", and only ] open("fiLe") will open it (open("file") will not, nor will the 14 other ] variations on that theme). ] In the lower right box, if you create "fiLe", there's no telling what it's ] stored as-- but most likely as "FILE" --and any of the 16 obvious variations ] on open("FilE") will open it.

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f = open ('fiLe', 'w')

$ directory f* Directory DSA3:[PYTHON.PYTHON-2_1A2CVS.VMS] FILE.;1

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f = open ('filE', 'r') f <open file 'filE', mode 'r' at 3E03B8>

This is on the default file system (ODS-2). Only very recent versions of OpenVMS Alpha (V7.2 and up) support the ODS-5 FS that has Windows-like behaviour (case-preserving,case-insensitive), but many sites don't use it (yet). Also, there are many older versions running in the field that don't get upgraded any time soon. ] The lower left box is a mix: creating "fiLe" stores "fiLe" in the platform ] directory, but you don't have to match case when opening it; any of the 16 ] obvious variations on open("FILe") work. Same here. ] What's proposed is to change the semantics of Python "import" statements, ] and there *only* in the lower left box. ] ] Support for MaxOSX HFS+, and for Cygwin, is new in 2.1, so nothing is ] changing there. What's changing is Windows behavior. Here are the current ] rules for import on Windows: ] ] 1. Despite that the filesystem is case-insensitive, Python insists on ] a case-sensitive match. But not in the way the upper left box works: ] if you have two files, FiLe.py and file.py on sys.path, and do ] ] import file ] ] then if Python finds FiLe.py first, it raises a NameError. It does ] *not* go on to find file.py; indeed, it's impossible to import any ] but the first case-insensitive match on sys.path, and then only if ] case matches exactly in the first case-insensitive match. For OpenVMS I have just changed 'import.c': MatchFilename() and some code around it is not executed. ] 2. An ugly exception: if the first case-insensitive match on sys.path ] is for a file whose name is entirely in upper case (FILE.PY or ] FILE.PYC or FILE.PYO), then the import silently grabs that, no matter ] what mixture of case was used in the import statement. This is ] apparently to cater to miserable old filesystems that really fit in ] the lower right box. But this exception is unique to Windows, for ] reasons that may or may not exist <frown>. I guess that is Windows-specific code? Something to do with 'allcaps8x3()'? ] 3. And another exception: if the envar PYTHONCASEOK exists, Python ] silently grabs the first case-insensitive match of any kind. The check is in 'check_case()', but there is no OpenVMS implementation (yet). ] So these Windows rules are pretty complicated, and neither match the Unix ] rules nor provide semantics natural for the native filesystem. That makes ] them hard to explain to Unix *or* Windows users. Nevertheless, they've ] worked fine for years, and in isolation there's no compelling reason to ] change them. ] However, that was before the MacOSX HFS+ and Cygwin ports arrived. They ] also have case-preserving case-insensitive filesystems, but the people doing ] the ports despised the Windows rules. Indeed, a patch to make HFS+ act like ] Unix for imports got past a reviewer and into the code base, which ] incidentally made Cygwin also act like Unix (but this met the unbounded ] approval of the Cygwin folks, so they sure didn't complain -- they had ] patches of their own pending to do this, but the reviewer for those balked). ] ] At a higher level, we want to keep Python consistent, and I in particular ] want Python to do the same thing on *all* platforms with case-preserving ] case-insensitive filesystems. Guido too, but he's so sick of this argument ] don't ask him to confirm that <0.9 wink>. What are you thinking about the 'unfortunate / OpenVMS' group ? Hey, it could be worse, could be 'brrrrrrrrrr'... ] The proposed new semantics for the lower left box: ] ] A. If the PYTHONCASEOK envar exists, same as before: silently accept ] the first case-insensitive match of any kind; raise ImportError if ] none found. ] ] B. Else search sys.path for the first case-sensitive match; raise ] ImportError if none found. ] ] #B is the same rule as is used on Unix, so this will improve cross-platform ] portability. That's good. #B is also the rule the Mac and Cygwin folks ] want (and wanted enough to implement themselves, multiple times, which is a ] powerful argument in PythonLand). It can't cause any existing ] non-exceptional Windows import to fail, because any existing non-exceptional ] Windows import finds a case-sensitive match first in the path -- and it ] still will. An exceptional Windows import currently blows up with a ] NameError or ImportError, in which latter case it still will, or in which ] former case will continue searching, and either succeed or blow up with an ] ImportError. ] ] #A is needed to cater to case-destroying filesystems mounted on Windows, and ] *may* also be used by people so enamored of "natural" Windows behavior that ] they're willing to set an envar to get it. That's their problem <wink>. I ] don't intend to implement #A for Unix too, but that's just because I'm not ] clear on how I *could* do so efficiently (I'm not going to slow imports ] under Unix just for theoretical purity). ] ] The potential damage is here: #2 (matching on ALLCAPS.PY) is proposed to be ] dropped. Case-destroying filesystems are a vanishing breed, and support for ] them is ugly. We're already supporting (and will continue to support) ] PYTHONCASEOK for their benefit, but they don't deserve multiple hacks in ] 2001. Would using unique names be an acceptable workaround? ] Flame at will. ] ] or-flame-at-tim-your-choice-ly y'rs - tim No flame intended. Not at will and not at tim.

--

Cameron Laird <claird@NeoSoft.com> Business: http://www.Phaseit.net Personal: http://starbase.neosoft.com/~claird/home.html

-- Uwe Zessin