Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Use "surrogateescape" error handler for sys.stdin and sys.stdout on UNIX for the C locale #64176

Closed
vstinner opened this issue Dec 13, 2013 · 38 comments
Labels
expert-unicode type-bug An unexpected behavior, bug, or error

Comments

@vstinner
Copy link
Member

vstinner commented Dec 13, 2013

BPO 19977
Nosy @loewis, @atsuoishimoto, @ncoghlan, @pitrou, @vstinner, @larryhastings, @jwilk, @ezio-melotti, @abadger, @bitdancer, @vadmium, @serhiy-storchaka
Files
  • c_locale_surrogateescape.patch
  • test_ls.py
  • Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

    Show more details

    GitHub fields:

    assignee = None
    closed_at = <Date 2014-04-27.23:57:39.901>
    created_at = <Date 2013-12-13.16:40:20.152>
    labels = ['type-bug', 'expert-unicode']
    title = 'Use "surrogateescape" error handler for sys.stdin and sys.stdout on UNIX for the C locale'
    updated_at = <Date 2017-12-18.14:31:51.323>
    user = 'https://github.com/vstinner'

    bugs.python.org fields:

    activity = <Date 2017-12-18.14:31:51.323>
    actor = 'vstinner'
    assignee = 'none'
    closed = True
    closed_date = <Date 2014-04-27.23:57:39.901>
    closer = 'vstinner'
    components = ['Unicode']
    creation = <Date 2013-12-13.16:40:20.152>
    creator = 'vstinner'
    dependencies = []
    files = ['33122', '33124']
    hgrepos = []
    issue_num = 19977
    keywords = ['patch']
    message_count = 38.0
    messages = ['206111', '206114', '206121', '206122', '206123', '206124', '206131', '206141', '206148', '206168', '207210', '207296', '207414', '210990', '213922', '213925', '213927', '213932', '213933', '215029', '215786', '215812', '215815', '217300', '217314', '217315', '217317', '217329', '217332', '217355', '217385', '217386', '217387', '284849', '284863', '284873', '284875', '308562']
    nosy_count = 15.0
    nosy_names = ['loewis', 'ishimoto', 'ncoghlan', 'pitrou', 'vstinner', 'larry', 'jwilk', 'ezio.melotti', 'a.badger', 'r.david.murray', 'Sworddragon', 'python-dev', 'martin.panter', 'serhiy.storchaka', 'bkabrda']
    pr_nums = []
    priority = 'normal'
    resolution = 'fixed'
    stage = None
    status = 'closed'
    superseder = None
    type = 'behavior'
    url = 'https://bugs.python.org/issue19977'
    versions = ['Python 3.5']

    @vstinner
    Copy link
    Member Author

    vstinner commented Dec 13, 2013

    When LANG=C is used to get the english language (which is a mistake, LC_CTYPE=C should be used instead) or when Python is started with an empty environment (no environment variable), Python gets the POSIX locale (aka "C locale") for the LC_CTYPE (encoding) locale.

    Standard streams use the locale encoding, which is usually ASCII with POSIX locale on most platforms (except on AIX: ISO 8859-1). In this case, data read from the OS (environment variables, command line arguments, filenames, etc.) may contain surrogate characters because of the internal usage of the surrogateescape error handler (see the PEP-383 for the rationale).

    The problem is that standard output uses the strict error handler, and so print() fails to display OS data like filenames.

    Example, "ls" command in Python:
    ---

    import os
    for name in sorted(os.listdir()): print(name)

    Try it with "LANG=C python ls.py" in a directory containing non-ASCII characters and you will get unicode errors.

    Issues bpo-19846 and bpo-19847 are examples of this annoyance.

    I propose to use also the surrogateescape error handler for sys.stdout if the POSIX locale is used for LC_CTYPE at startup. Attached patch implements this idea.

    With the patch, "LANG=C python ls.py" almost works as filenames and stdout are byte streams, even if the Unicode type is used.

    @vstinner
    Copy link
    Member Author

    vstinner commented Dec 13, 2013

    Oh, in fact, sys.stdin is also modified by the patch (as I expected).

    @vstinner vstinner changed the title Use "surrogateescape" error handler for sys.stdout on UNIX for the C locale Use "surrogateescape" error handler for sys.stdin and sys.stdout on UNIX for the C locale Dec 13, 2013
    @Sworddragon
    Copy link
    Mannequin

    Sworddragon mannequin commented Dec 13, 2013

    What would happen if we call this example script with LANG=C on the patch?:

    ---

    import os
    for name in sorted(os.listdir('ä')):
    	print(name)

    Would it throw an exception on os.listdir('ä')?

    @vstinner
    Copy link
    Member Author

    vstinner commented Dec 13, 2013

    test_ls.py: test script producing invalid filenames and then trying to display them into stdout.

    Output with UTF-8 locale, UTF-8 terminal and Python 3.3 (or unpatched 3.4, it's the same):

    ascii.txt
    <UnicodeError 'invalid_utf8:\udcff.txt'>
    <UnicodeError 'latin1:\udce9.txt'>
    utf8:é€.txt

    Output with C locale (ASCII), UTF-8 terminal and Python 3.3:

    ascii.txt
    <UnicodeError 'invalid_utf8:\udcff.txt'>
    <UnicodeError 'latin1:\udce9.txt'>
    <UnicodeError 'utf8:\udcc3\udca9\udce2\udc82\udcac.txt'>

    Output with C locale (ASCII), UTF-8 terminal and patched Python 3.4:

    ascii.txt
    invalid_utf8:�.txt
    latin1:�.txt
    utf8:é€.txt

    You get no Unicode error with LANG=C, but you get mojibake instead.

    @vstinner
    Copy link
    Member Author

    vstinner commented Dec 13, 2013

    os.fsencode(text) always fail if text cannot be encoded to sys.getfilesystemencoding(). surrogateescape doesn't help here.

    Your example is "artificial", you should not get 'ä'. All OS data is decoded from the filesystem encoding using the surrogateescape error handler (except on Windows, where strict is used, but it's a different story, Python uses Unicode functions when available so don't worry). So all these data can always be encoded back to bytes using os.fsencode().

    More generally, os.fsencode(os.fsdecode(read_data)) == read_data is always true on Unix, with any filesystem (locale) encoding.

    You may get Unicode data from other sources like files or a GUI, but I don't see what can be done here.

    @pitrou
    Copy link
    Member

    pitrou commented Dec 13, 2013

    When LANG=C is used to get the english language (which is a mistake,
    LC_CTYPE=C should be used instead)

    I think you mean LC_MESSAGES=C here.
    (but it's not only about the English language; it's also about other locale parameters such as number formatting)

    I think we should start thinking about making utf-8 the default filesystem encoding in 3.5 (under Unix).

    @bitdancer
    Copy link
    Member

    bitdancer commented Dec 13, 2013

    Reintroducing moji-bake intentionally doesn't sound like a particularly good idea, wasn't that what python3 was supposed to help prevent?

    It does seem like a utf-8 default is the Way of the Future. Or even the present, most places.

    @abadger
    Copy link
    Mannequin

    abadger mannequin commented Dec 13, 2013

    My impression was that python3 was supposed to help get rid of UnicodeError tracebacks, not mojibake. If mojibake was the problem then we should never have gone down the surrogateescape path for input.

    @serhiy-storchaka
    Copy link
    Member

    serhiy-storchaka commented Dec 13, 2013

    Mojibake in input can cause decoding error in other application which consumes output of Python script. In some cases this can be even worse thin UnicodeError in producer.

    But for C locale this makes sense. I think we should try this experiment in 3.5. There will be much time for testing before 3.5 beta 1.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Dec 14, 2013

    Getting rid of mojibake was the goal, surrogateescape was about dealing with cases where the "avoid mojibake" checks were spuriously breaking round-tripping between OS APIs due to other configuration errors (with LANG=C being set, or LANG not being set at all being the main problem). Other "high mojibake risk" power tools (like changing the encoding of an already open stream) are likely to return in the future, since there *are* cases where they're the right answer (e.g. you can't right an iconv equivalent in Python 3 at the moment, we need bpo-15216 implemented before that will be possible).

    +1 for this solution - see bpo-19846 for the long discussion which got us to this point (there are a few unrelated tangents, a couple of them my fault, but this is definitely an improvement over the status quo.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Jan 3, 2014

    Larry: I'm assuming it's way too late to make a change like this for the 3.4 release?

    Slavek: assuming this change is made for 3.5 upstream, we may want to look at backporting it as a 3.4 patch in Fedora (as part of the Python-3-by-default project). Otherwise it's very easy to provoke Python 3 into throwing Unicode errors when attempting to print data provided by the OS.

    @ncoghlan ncoghlan added the type-bug An unexpected behavior, bug, or error label Jan 3, 2014
    @larryhastings
    Copy link
    Contributor

    larryhastings commented Jan 4, 2014

    Yeah, unless there was a *huge* amount of support for changing this, it's way too late for 3.4.

    @bkabrda
    Copy link
    Mannequin

    bkabrda mannequin commented Jan 6, 2014

    Nick: Sure, once there is an upstream solution that people have agreed on, I'll look into backporting it, NP. Thanks for letting me know about this.

    @vstinner
    Copy link
    Member Author

    vstinner commented Feb 11, 2014

    Reintroducing moji-bake intentionally doesn't sound like a particularly good idea, wasn't that what python3 was supposed to help prevent?

    Sometimes practicality beats purity :-(

    I tried to convince users that their computer was "not well configured", they always replied that Python 3 fails where Perl, PHP, Python 2, C, etc. "just work".

    @python-dev
    Copy link
    Mannequin

    python-dev mannequin commented Mar 18, 2014

    New changeset bc06f67234d0 by Victor Stinner in branch 'default':
    Issue bpo-19977: When the LC_TYPE locale is the POSIX locale (C locale),
    http://hg.python.org/cpython/rev/bc06f67234d0

    @vstinner
    Copy link
    Member Author

    vstinner commented Mar 18, 2014

    Test failing on "x86 OpenIndiana 3.x" buildbot:

    http://buildbot.python.org/all/builders/x86%20OpenIndiana%203.x/builds/7939/steps/test/logs/stdio

    ======================================================================
    FAIL: test_forced_io_encoding (test.test_capi.EmbeddingTests)
    ----------------------------------------------------------------------

    Traceback (most recent call last):
      File "/export/home/buildbot/32bits/3.x.cea-indiana-x86/build/Lib/test/test_capi.py", line 352, in test_forced_io_encoding
        self.assertEqual(out.strip(), expected_output)
    AssertionError: '--- [79 chars]646:surrogateescape\nstdout: 646:surrogateesca[576 chars]lace' != '--- [79 chars]646:strict\nstdout: 646:strict\nstderr: 646:ba[540 chars]lace'
      --- Use defaults 

      Expected encoding: default
      Expected errors: default
    - stdin: 646:surrogateescape
    - stdout: 646:surrogateescape
    + stdin: 646:strict
    + stdout: 646:strict
      stderr: 646:backslashreplace
      --- Set errors only 

    Expected encoding: default
    Expected errors: surrogateescape
    stdin: 646:surrogateescape
    stdout: 646:surrogateescape
    stderr: 646:backslashreplace
    --- Set encoding only ---

      Expected encoding: latin-1
      Expected errors: default
    - stdin: latin-1:surrogateescape
    - stdout: latin-1:surrogateescape
    + stdin: latin-1:strict
    + stdout: latin-1:strict
      stderr: latin-1:backslashreplace
      --- Set encoding and errors 

    Expected encoding: latin-1
    Expected errors: surrogateescape
    stdin: latin-1:surrogateescape
    stdout: latin-1:surrogateescape
    stderr: latin-1:backslashreplace

    @vstinner
    Copy link
    Member Author

    vstinner commented Mar 18, 2014

    New behaviour:

    $ mkdir z
    $ touch z/abcé
    $ LC_CTYPE=C ./python -c 'import os; print(os.listdir("z")[0])'
    abcé

    Old behaviour, before the change (test with Python 3.3):

    $ LC_CTYPE=C python3 -c 'import os; print(os.listdir("z")[0])'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    UnicodeEncodeError: 'ascii' codec can't encode characters in position 3-4: ordinal not in range(128)

    @python-dev
    Copy link
    Mannequin

    python-dev mannequin commented Mar 18, 2014

    New changeset 3589980c98de by Victor Stinner in branch 'default':
    Issue bpo-19977, bpo-19036: Always include <locale.h> in pythonrun.c
    http://hg.python.org/cpython/rev/3589980c98de

    New changeset 94d5025c70a3 by Victor Stinner in branch 'default':
    Issue bpo-19977: Enable test_c_locale_surrogateescape() on Windows
    http://hg.python.org/cpython/rev/94d5025c70a3

    @python-dev
    Copy link
    Mannequin

    python-dev mannequin commented Mar 18, 2014

    New changeset c9905e802042 by Victor Stinner in branch 'default':
    Issue bpo-19977: Fix test_capi when LC_CTYPE locale is POSIX
    http://hg.python.org/cpython/rev/c9905e802042

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Mar 28, 2014

    This seems to be working on the buildbots for 3.5 now (buildbot failures appear to be due to other issues).

    However, I'd still like to discuss the idea of backporting this to 3.4.1.

    From a Fedora point of view, it's still *very* easy to flip an environment into POSIX mode, so even if the system is appropriately configured to use UTF-8 everywhere, Python 3.4 may still blow up if a script or application ends up running under the POSIX locale.

    That has long made Toshio nervous about the migration of core services to Python 3 (https://fedoraproject.org/wiki/Changes/Python_3_as_Default), and his concerns make sense to me, as that migration covers little things like the installer, package manager, post-image install initialisation, etc. I'm not sure the Fedora team can deliver on the "Users shouldn't notice any changes, except that packages in minimal buildroot and on LiveCD will be python3-, not python-." aspect of the change proposal without this behavioural tweak in the 3.4 series as well.

    Note that this *isn't* a blocker for the migration - if it was, it would be mentioned in the Fedora proposal. However, I think there's a risk to the Fedora user experience if the status quo remains in place for the life of Python 3.4, and I'd hate for the first encounter Fedora users have with Python 3 to be inexplicable tracebacks from components that have been migrated.

    @vstinner
    Copy link
    Member Author

    vstinner commented Apr 9, 2014

    "However, I'd still like to discuss the idea of backporting this to 3.4.1."

    THe idea of doing this change in Python 3.5 is that I have no idea of the risk of regression. To backport such change in a minor version (3.4.1), I would feel more confident with user tests of Python 3.5 or patched Python 3.4.

    "That has long made Toshio nervous about the migration of core services to Python 3 (https://fedoraproject.org/wiki/Changes/Python_3_as_Default), and his concerns make sense to me, as that migration covers little things like the installer, package manager, post-image install initialisation, etc. "

    Which programs in this test are or may be running with the POSIX locale?

    Fedora doesn't use en_US.utf8 locale by default?

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 9, 2014

    The default locale on Fedora is indeed UTF-8 these days - the problem is that *users* are used to being able to use "LANG=C" to force the POSIX locale (whether for testing purposes or other reasons), and that currently means system utilities written in Python may fail in such situations if used with UTF-8 data from the filesystem (or elsewhere). (I believe there may also be other cases where POSIX mandates the use of the C locale, but Toshio would be in a better position than I am to confirm whether or not that is actually the case).

    So perhaps this is best left in a "wait & see" mode for now - as the Fedora migration to Python 3 progresses, if the folks working on that find specific utilities where the Python 3.4 standard stream handling in the C locale appears problematic, then Slavek & Toshio can bring them up here.

    The counterargument is that if we're going to change it, 3.4.1 would be a better time frame than 3.4.2. In that case, the task of identifying specific Fedora utilities of concern still falls back on Toshio & Slavek, but it would be a matter of going hunting for them specifically *now*, rather than waiting until they come up over the course of the migration.

    @vstinner
    Copy link
    Member Author

    vstinner commented Apr 9, 2014

    The default locale on Fedora is indeed UTF-8 these days - the problem is that *users* are used to being able to use "LANG=C" to force the POSIX locale (whether for testing purposes or other reasons), and that currently means system utilities written in Python may fail in such situations if used with UTF-8 data from the filesystem (or elsewhere). (I believe there may also be other cases where POSIX mandates the use of the C locale, but Toshio would be in a better position than I am to confirm whether or not that is actually the case).

    A common situation where you get a C locale is for programs started by
    a crontab. If I remember correctly, these programs start with the C
    locale, instead of the "system" (user?) locale.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 27, 2014

    Additional environments where the system misreports the encoding to use (courtesy of Armin Ronacher & Graham Dumpleton on Twitter): upstart, Salt, mod_wsgi.

    Note that for more complex applications (e.g. integrated web UIs, socket servers, sending email), round tripping to the standard streams won't be enough - what we really need is a better "source of truth" as to the real system encoding when POSIX compliant systems provide incorrect configuration data to the interpreter.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 27, 2014

    bpo-21368 now suggests looking for /etc/locale.conf before falling back to ASCII+surrogateescape.

    @pitrou
    Copy link
    Member

    pitrou commented Apr 27, 2014

    We should not overcomplicate this. I suggest that we simply use utf-8 under the C locale.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 27, 2014

    If you can convince Stephen Turnbull that's a good idea, sure. It's
    probably more likely to be the right thing than "ASCII" or "ASCII +
    surrogateescape", but in the absence of hard data, he's in a better
    position than we are to judge the likely impact of that, at least in Japan.

    I'm also going to hunt around on freedesktop.org to see if there's anything
    more general there on the topic of encodings.

    @vstinner
    Copy link
    Member Author

    vstinner commented Apr 27, 2014

    We should not overcomplicate this. I suggest that we simply use utf-8 under the C locale.

    Do you mean utf8/strict or utf8/surrogateescape?

    utf8/strict doesn't work (os.listdir raises an unicode error) if your
    system is configured to use latin1 (ex: filenames are stored in this
    encoding), but unfortunately your program is running in an empty
    environment (so will use the POSIX locale).

    @vstinner
    Copy link
    Member Author

    vstinner commented Apr 27, 2014

    We should not overcomplicate this. I suggest that we simply use utf-8 under the C locale.

    Please open a new issue if you would prefer UTF-8. You will have to solve different technical issues. I tried to list some of them in issues bpo-19846 and bpo-19847.

    In short, you should always decode and encode "OS data" with the same encoding. Python "file system encoding" is the locale encoding because in some places, PyUnicode_DecodeLocaleAndSize is used (ex: to decode PYTHONWARNINGS environment variable). A common location is PyUnicode_DecodeFSDefaultAndSize() before the Python codec is loaded. See also _Py_wchar2char() and _Py_char2wchar() functions which use the locale encoding and are used in many places.

    I'm now closing the issue because the initial point (use surrogateescape error handler) is implemented in Python 3.5, and backporting such major change in Python 3.4 branch is risky right now.

    @pitrou
    Copy link
    Member

    pitrou commented Apr 28, 2014

    > We should not overcomplicate this. I suggest that we simply use utf-8 under the C locale.

    Do you mean utf8/strict or utf8/surrogateescape?

    utf8/strict doesn't work (os.listdir raises an unicode error) if your
    system is configured to use latin1 (ex: filenames are stored in this
    encoding), but unfortunately your program is running in an empty
    environment (so will use the POSIX locale).

    The issue is about stdin and stdout, I'm not sure why os.listdir would
    be affected.

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 28, 2014

    Victor was referring to code like "print(os.listdir())". Those are the
    motivating cases for ensuring round trips from system APIs to the standard
    streams work correctly.

    There's also the problem that sys.argv currently relies on the locale
    encoding directly, because the filesystem encoding hasn't been worked out
    at that point (see bpo-8776). So this current change will also make
    "print(sys.argv)" work more reliably in the POSIX locale.

    The conclusion I have come to is that any further decoupling of Python 3
    from the locale encoding will actually depend on getting the PEP-432
    bootstrapping changes implemented, reviewed and the PEP approved, so we
    have more interpreter infrastructure in place by the time the interpreter
    starts trying to figure out all these boundary encoding issues.

    @pitrou
    Copy link
    Member

    pitrou commented Apr 28, 2014

    The conclusion I have come to is that any further decoupling of Python 3
    from the locale encoding will actually depend on getting the PEP-432
    bootstrapping changes implemented, reviewed and the PEP approved, so we
    have more interpreter infrastructure in place by the time the interpreter
    starts trying to figure out all these boundary encoding issues.

    Yeah. My proposal had more to do with the fact that we should some day
    switch to utf-8 by default on all POSIX systems, regardless of what the
    system advertises as "best encoding".

    @ncoghlan
    Copy link
    Contributor

    ncoghlan commented Apr 28, 2014

    Antoine Pitrou added the comment:

    Yeah. My proposal had more to do with the fact that we should some day
    switch to utf-8 by default on all POSIX systems, regardless of what the
    system advertises as "best encoding".

    Yeah, that seems like a plausible future to me as well, and knowing it's a
    step along that path actually gives me more motivation to get back to
    working on the startup issues :)

    @Sworddragon
    Copy link
    Mannequin

    Sworddragon mannequin commented Jan 6, 2017

    Bug bpo-28180 has caused me to make a look at the "encoding" issue this and the tickets before have tried to solve more or less. Being a bit unsure what the root cause and intention for all this was I'm now at a point to actually check this ticket. Here is an example code (executed with Python 3.5.3 RC1 by having LANG set to C):

    import sys
    sys.stdout.write('ä')

    I thought with the surrogateescape error handler now being used for sys.stdout this would not throw an exception but I'm getting this:

    UnicodeEncodeError: 'ascii' codec can't encode character '\xe4' in position 0: ordinal not in range(128)

    @vstinner
    Copy link
    Member Author

    vstinner commented Jan 6, 2017

    "I thought with the surrogateescape error handler now being used for sys.stdout this would not throw an exception but I'm getting this: (...)"

    Please see the two recently proposed PEP: Nick's PEP-538 and my PEP-540, both propose (two different) solutions to your issue, especially for the POSIX locale (aka "C" locale).

    @Sworddragon
    Copy link
    Mannequin

    Sworddragon mannequin commented Jan 6, 2017

    The point is this ticket claims to be using the surrogateescape error handler for sys.stdout and sys.stdin for the C locale. I have never used surrogateescape explicitly before and thus have no experience for it and consulting the documentation mentions throwing an exception only for the strict error handler. I don't see anything that would make me think that surrogateescape would throw here an exception too. But maybe I'm just missing something.

    @vstinner
    Copy link
    Member Author

    vstinner commented Jan 6, 2017

    But maybe I'm just missing something.

    This issue fixed exactly one use case: "List a directory into stdout" (similar to the UNIX "ls" or Windows "dir" commands):
    https://www.python.org/dev/peps/pep-0540/#list-a-directory-into-stdout

    Your use case is more "Display Unicode characters into stdout":
    https://www.python.org/dev/peps/pep-0540/#display-unicode-characters-into-stdout

    This use case is not supported by the issue. It should be fixed by PEP-538 or PEP-540.

    Please join the happy discussion on the python-ideas mailing list to discuss how to "force UTF-8": this issue is closed, you shouldn't add new comments (other people will not see your comments).

    @vstinner
    Copy link
    Member Author

    vstinner commented Dec 18, 2017

    Follow-up: the PEP-538 (bpo-28180) and PEP-540 (bpo-29240) have been accepted and implemented in Python 3.7!

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
    Labels
    expert-unicode type-bug An unexpected behavior, bug, or error
    Projects
    None yet
    Development

    No branches or pull requests

    6 participants