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As discussed on issue8610, we need a way to override the automatic detection of the file system encoding - for much the same reasons we also do for the I/O encoding: the detection mechanism isn't fail-safe.
We should add a new environment variable with the same functionality as PYTHONIOENCODING:
 PYTHONFSENCODING: Encoding[:errors] used for file system.

Here you have a patch. It adds tests in test_sys.
The tests are skipped on a non-ascii Python executable path because of #8611 (see #9425).

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@haypocalc.com> added the comment:
> 
> Here you have a patch. It adds tests in test_sys.
> 
> The tests are skipped on a non-ascii Python executable path because of #8611 (see #9425).
Thanks for the patch.
A couple of notes:
 * The command line -h explanation is missing from the patch.
 * The documentation should mention that the env var is only
 read once; subsequent changes to the env var are not seen
 by Python
 * If the codec lookup fails, Python should either issue a warning
 and then ignore the env var (using the get_codeset() API).
 * Unrelated to the env var, but still important: if get_codeset()
 does not return a known codec, Python should issue a warning
 before falling back to the default setting. Otherwise, a
 Python user will never know that there's an issue and this
 make debugging a lot harder.
We should also add a new sys.setfilesystemencoding()
function to make changes possible after Python startup. This
would have to go on a separate ticket, though. Or is there
some concept preventing this ?

> The command line -h explanation is missing from the patch.
done
> The documentation should mention that the env var is only
> read once; subsequent changes to the env var are not seen
> by Python
I copied the PYTHONIOENCODING doc which doesn't mention that. Does Python re-read other environment variables at runtime? Anyway, I changed the doc to:
+ If this is set before running the intepreter, it overrides the encoding used
+ for the filesystem encoding (see :func:`sys.getfilesystemencoding`).
I also changed PYTHONIOENCODING doc. Is it better?
> If the codec lookup fails, Python should either issue a warning
Ok, done. I patched also get_codeset() and get_codec_name() to always set a Python error.
> ... and then ignore the env var (using the get_codeset() API).
Good idea, done.
> Unrelated to the env var, but still important: if get_codeset()
> does not return a known codec, Python should issue a warning
> before falling back to the default setting. Otherwise, a
> Python user will never know that there's an issue and this
> make debugging a lot harder.
It does already write a message to stderr, but it doesn't explain why it failed.
I changed initfsencoding() to display two messages on get_codeset() error. First explain why get_codeset() failed (with the Python error) and then say that we fallback to utf-8.
Full example (PYTHONFSENCODING error and simulated get_codeset() error):
---
PYTHONFSENCODING is not a valid encoding:
LookupError: unknown encoding: xxx
Unable to get the locale encoding:
ValueError: CODESET is not set or empty
Unable to get the filesystem encoding: fallback to utf-8
---
> We should also add a new sys.setfilesystemencoding() ...
No, I plan to REMOVE this function. sys.setfilesystemencoding() is dangerous because it introduces a lot of inconsistencies: this function is unable to reencode all filenames in all objects (eg. Python is unable to find filenames in user objects or 3rd party libraries). Eg. if you change the filesystem from utf8 to ascii, it will not be possible to use existing non-ascii (unicode) filenames: they will raise UnicodeEncodeError. As sys.setdefaultencoding() in Python2, I think that sys.setfilesystemencoding() is the root of evil :-)
At startup, initfsencoding() sets the filesystem encoding using the locale encoding. Even for the startup process (with very few objects), it's very hard to find all filenames:
 - sys.path
 - sys.meta_path
 - sys.modules
 - sys.executable
 - all code objects
 - and I'm not sure that the list is complete
See #9630 for the details.
To remove sys.setfilesystemencoding(), I already patched PEP 383 tests (r84170) and I will open a new issue. But it's maybe better to commit both changes (remove the function and PYTHONFSENCODING) at the same time.

> To remove sys.setfilesystemencoding(), ... I will open a new issue
done, issue #9632 

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@haypocalc.com> added the comment:
> 
>> The command line -h explanation is missing from the patch.
> 
> done
> 
>> The documentation should mention that the env var is only
>> read once; subsequent changes to the env var are not seen
>> by Python
> 
> I copied the PYTHONIOENCODING doc which doesn't mention that. Does Python re-read other environment variables at runtime? Anyway, I changed the doc to:
> 
> + If this is set before running the intepreter, it overrides the encoding used
> + for the filesystem encoding (see :func:`sys.getfilesystemencoding`).
> 
> I also changed PYTHONIOENCODING doc. Is it better?
Yes, thanks.
>> If the codec lookup fails, Python should either issue a warning
> 
> Ok, done. I patched also get_codeset() and get_codec_name() to always set a Python error.
> 
>> ... and then ignore the env var (using the get_codeset() API).
> 
> Good idea, done.
> 
>> Unrelated to the env var, but still important: if get_codeset()
>> does not return a known codec, Python should issue a warning
>> before falling back to the default setting. Otherwise, a
>> Python user will never know that there's an issue and this
>> make debugging a lot harder.
> 
> It does already write a message to stderr, but it doesn't explain why it failed.
> 
> I changed initfsencoding() to display two messages on get_codeset() error. First explain why get_codeset() failed (with the Python error) and then say that we fallback to utf-8.
> 
> Full example (PYTHONFSENCODING error and simulated get_codeset() error):
> ---
> PYTHONFSENCODING is not a valid encoding:
> LookupError: unknown encoding: xxx
> Unable to get the locale encoding:
> ValueError: CODESET is not set or empty
> Unable to get the filesystem encoding: fallback to utf-8
> ---
Looks good !
>> We should also add a new sys.setfilesystemencoding() ...
> 
> No, I plan to REMOVE this function. sys.setfilesystemencoding() is dangerous because it introduces a lot of inconsistencies: this function is unable to reencode all filenames in all objects (eg. Python is unable to find filenames in user objects or 3rd party libraries). Eg. if you change the filesystem from utf8 to ascii, it will not be possible to use existing non-ascii (unicode) filenames: they will raise UnicodeEncodeError. As sys.setdefaultencoding() in Python2, I think that sys.setfilesystemencoding() is the root of evil :-)
Sorry, I wasn't aware we had such a function (and was looking at the
wrong file so didn't find it).
> At startup, initfsencoding() sets the filesystem encoding using the locale encoding. Even for the startup process (with very few objects), it's very hard to find all filenames:
> - sys.path
> - sys.meta_path
> - sys.modules
> - sys.executable
> - all code objects
> - and I'm not sure that the list is complete
> 
> See #9630 for the details.
> 
> To remove sys.setfilesystemencoding(), I already patched PEP 383 tests (r84170) and I will open a new issue. But it's maybe better to commit both changes (remove the function and PYTHONFSENCODING) at the same time.

Commited to 3.2 as r84182.

Oh, I realized that PYTHONFSENCODING is ignored on Windows and Mac OS X. r84201 and r84202 fix test_sys, and r84203 fixes the documentation and Python usage (hide PYTHONFSENCODING variable in Python help on Windows and Mac OS X).
We might allow to override the filesystem encoding on Windows, but I don't think that it is a good idea because third party libraries will use anyway the mbcs encoding.

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@haypocalc.com> added the comment:
> 
> Oh, I realized that PYTHONFSENCODING is ignored on Windows and Mac OS X. r84201 and r84202 fix test_sys, and r84203 fixes the documentation and Python usage (hide PYTHONFSENCODING variable in Python help on Windows and Mac OS X).
This has to be changed: The env var needs to be respected on all
platforms.

> > Oh, I realized that PYTHONFSENCODING is ignored on Windows and Mac OS X.
> > r84201 and r84202 fix test_sys, and r84203 fixes the documentation and
> > Python usage (hide PYTHONFSENCODING variable in Python help on Windows
> > and Mac OS X).
> 
> This has to be changed: The env var needs to be respected on all
> platforms.
I don't think so.
On Mac OS X, you cannot create a file with an invalid utf-8 name. The VFS uses 
utf-8:
http://developer.apple.com/mac/library/qa/qa2001/qa1173.html
Use a different encoding will raise error for the first non-ascii filename.
--
About Windows, Python3 uses the wide character API of Windows, except in some 
functions using third party libraries only providing a bytes API (eg. 
openssl). filenames are stored as unicode, even on removable media like CD-Rom 
or USB keys. I don't get the usecase here. Why would you like to change the 
filesystem encoding on Windows?

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@haypocalc.com> added the comment:
> 
>>> Oh, I realized that PYTHONFSENCODING is ignored on Windows and Mac OS X.
>>> r84201 and r84202 fix test_sys, and r84203 fixes the documentation and
>>> Python usage (hide PYTHONFSENCODING variable in Python help on Windows
>>> and Mac OS X).
>>
>> This has to be changed: The env var needs to be respected on all
>> platforms.
> 
> I don't think so.
> 
> On Mac OS X, you cannot create a file with an invalid utf-8 name. The VFS uses 
> utf-8:
> http://developer.apple.com/mac/library/qa/qa2001/qa1173.html
> 
> Use a different encoding will raise error for the first non-ascii filename.
> 
> --
> 
> About Windows, Python3 uses the wide character API of Windows, except in some 
> functions using third party libraries only providing a bytes API (eg. 
> openssl). filenames are stored as unicode, even on removable media like CD-Rom 
> or USB keys. I don't get the usecase here. Why would you like to change the 
> filesystem encoding on Windows?
Ok, point taken.
Just please make sure that on other platforms such as BSD, Solaris,
AIX, etc. that don't have this special Python support
the env vars are honored.

Le jeudi 19 août 2010 22:40:53, vous avez écrit :
> Just please make sure that on other platforms such as BSD, Solaris,
> AIX, etc. that don't have this special Python support
> the env vars are honored.
I added much more tests on the filesystem encoding:
 - (test_os) FSEncodingTests.test_encodings() tests different encoding values 
and check for some known values
 - (test_sys) SysModuleTest.test_pythonfsencoding() tests Python with C locale 
and check that the FS encoding is ascii, and test that setting 
PYTHONFSENCODING is understood by Python (run python with "import sys; 
print(sys.getfilesystemencoding())" and compare the output)
These tests are skipped on Windows and Mac OS X. I also patched the doc 
(what's new / cmdline) to explain that PYTHONFSENCODING is not available 
(ignored) on these OSes.

This is still an issue on some buildbots:
 - since r84224 on OS X (PPC Leopard, x86 Tiger)
 - since r84182 on sparc solaris10 gcc, x86 FreeBSD, x86 FreeBSD 7.2
The issue was fixed in r84201, r84202, r84203 for OS X buildbots only, but since r84224 it is failing again.

I'm working on a fix for test_sys failure. test_os should not fail anymore.

In an up to date checkout of py3k on Gentoo linux with LC_CTYPE=en_US.UTF-8, I get a failure in test_sys:
======================================================================
FAIL: test_pythonfsencoding (test.test_sys.SysModuleTest)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/rdmurray/python/py3k/Lib/test/test_sys.py", line 605, in test_pythonfsencoding
 self.check_fsencoding(get_fsencoding(env), 'ascii')
 File "/home/rdmurray/python/py3k/Lib/test/test_sys.py", line 573, in check_fsencoding
 self.assertEqual(fs_encoding, expected)
AssertionError: 'utf-8' != 'ascii'
- utf-8
+ ascii

Setting LC_ALL instead of LANG in the test fixes the problem.

r84308 should fix the last problems on Mac OS X, FreeBSD and Solaris.
The last failure on test_sys is on Windows with test_undecodable_code (TypeError: Type str doesn't support the buffer API), which is unrelated.
Reopen the issue if you see new failures.

test_sys is still failing on my system where LC_CTYPE only is set to utf-8. Victor, do you want me to apply the LANG->LC_ALL change to the test?

> test_sys is still failing on my system where LC_CTYPE 
> only is set to utf-8
Oh yes, test_sys fails if LC_ALL or LC_CTYPE is a locale using a different encoding than ascii (eg. LC_ALL=fr_FR.utf8). Fixed by r84314.