On Sun, Jul 14, 2013 at 8:16 AM, Itamar Turner-Trauring wrote: On 07/13/2013 10:00 PM, Harry Bock wrote: Hi all, My name is Harry Bock. I'm interested in helping out porting Twisted to
Python 3, and I've popped in IRC a few times to introduce myself and ask a
few questions. A few developers agreed that working on trial dependencies
would be a big help. In doing some porting work on trial, I stumbled upon a previous porting
effort (possibly by Itamar?) for twisted.python.filepath and related
modules. It seemed like the porting effort included forcing all pathname
inputs to be byte strings instead of native strings. You imply that this was a change, somehow, but it wasn't. The API was
*always* bytes and it continues to be bytes on Python 3. Ah, I understand now. Since the native string type was used in Python 2,
it follows that in Python 3 the API should be bytes. It's a common Python 3 porting mistake to change everything from bytes to
unicode just because. E.g. Python standard library does this in many places
for no good reason, resulting in bugs that are still being fixed (
http://bugs.python.org/**issue12411 http://bugs.python.org/issue12411)
or APIs that are less useful (zipfile docs explicitly state that there is
no standard encoding in zip files, but Python 3 zipfile module only
supports one specific encoding because they switched to Unicode and didn't
bother reading the module's own docs). Our goal in porting was backwards
compatibility with Python 2 code, so porters don't have to change
everything, and correctness. And, in this particular case, to get something
working in the minimal amount of time - *adding* Unicode support is useful
and should be done. After some investigation, I believe this is the wrong approach, but I wanted to start a discussion here first. Some thoughts: (a) As of Python 3.3, use of the ANSI API in Windows is deprecated[1], so
many functions in os and os.path raise DeprecationWarning when given byte
strings as input. Although win32 is not an initial target of the porting
effort, we'll have to support it eventually and the API should be supported
before then. (b) Misunderstandings at the application level about the underlying
filesystem's path encoding is not the problem of the Twisted API. Correct
me if I'm wrong, but that's the responsibility of the system administrator
or individual user (at least on UNIX) to set the LANG environment variable,
or for the application to call setlocale(3) to explicitly override it. Given operating systems that don't really know about encodings on the
filesystem level, forcing everything to be unicode doesn't make sense. I'm
pretty sure you can end up with files in multiple different Unicode
encodings on same filesystem on Linux, for example. This is very true and I didn't consider it in my initial investigation.
While I think it would be uncommon to have files in multiple encodings on
the same filesystem, it certainly would not be rare - to Tristan's point,
copying names from filesystem to filesystem could easily result in multiple
encodings. The operating system may not need to understand the encodings,
but applications do to display them correctly, Which leads to your last
point... Thus, my vote is that on Python 2.x, Twisted should accept either the native str or unicode types for path names, and on Python 3.x, only accept
the str type to prevent deprecation issues with system calls. I have a
patch set that will make this happen including unittest modifications; if
there's a consensus I'm happy to open a ticket and submit the patches. The ideal situation would be to support bytes and Unicode on Python 2
*and* Python 3, for maximum compatibility. Even if deprecated on Windows,
filesystem operations on Python 3 still do accept bytes (and they're not
deprecated elsewhere). Given existing code that already takes bytes,
switching to only doing Unicode on Python 3 would not be backwards
compatible, so we can't really do that without a bunch of deprecation
warnings and a few releases. Instead we should just do what Python does: if
you start with bytes path you always get back bytes, if you start with
Unicode path you always get back Unicode. Yes, you're right, that's probably the best solution. It would not be
terribly hard to do so - then application developers can choose whether to
defer to the local user's interpretation of the setting, or explicitly use
byte paths. Thanks so much for your input!
Is this something I can open a ticket for? ______________________________**_________________
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