Mailman 3 January 2017 - Python-ideas

How to respond to trolling (Guido van Rossum)
by Simon Lovell Jan. 13, 2017

Jan. 13, 2017

I feel I have to respond to this one. More than half of what I suggested could have and should be implemented. In particular the truthiness of non-boolean data and the lack of a reasonable SQL syntax. Several other points have been discussed endlessly on the internet but without a satisfactory (IMO) answer being given. I don't know what is meant by some insults having been thrown in. Calling truthiness of non boolean data "Ugly" is an insult? It is ugly. Yes, I should have double … [View More]

8 8

RFC: PEP 540 version 3 (Add a new UTF-8 mode)
by Victor Stinner Jan. 13, 2017

Jan. 13, 2017

Hi, I also implemented my PEP 540, you can now test it! Use the latest patch attached to: http://bugs.python.org/issue29240 I made multiple changes since the first version of my PEP: * The UTF-8 Strict mode now only uses strict for inputs and outputs: it keeps surrogateescape for operating system data. Read the "Use the strict error handler for operating system data" alternative for the rationale. * The POSIX locale now enables the UTF-8 mode. See the "Don't modify the encoding of the … [View More]

7 18

PEP 540: Add a new UTF-8 mode
by Victor Stinner Jan. 13, 2017

Jan. 13, 2017

Hi, Nick Coghlan asked me to review his PEP 538 "Coercing the legacy C locale to C.UTF-8": https://www.python.org/dev/peps/pep-0538/ Nick wants to change the default behaviour. I'm not sure that I'm brave enough to follow this direction, so I proposed my old "-X utf8" command line idea as a new PEP: add a new UTF-8 mode, *disabled by default*. These 2 PEPs are the follow-up of the Windows PEP 529 (Change Windows filesystem encoding to UTF-8) and the issue #19977 (Use "surrogateescape" error … [View More]handler for sys.stdin and sys.stdout on UNIX for the C locale). The topic (switching to UTF-8 on UNIX) is actively discussed on: http://bugs.python.org/issue28180 Read the PEP online (HTML): https://www.python.org/dev/peps/pep-0540/ Victor PEP: 540 Title: Add a new UTF-8 mode Version: $Revision$ Last-Modified: $Date$ Author: Victor Stinner <victor.stinner(a)gmail.com> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 5-January-2016 Python-Version: 3.7 Abstract ======== Add a new UTF-8 mode, opt-in option to use UTF-8 for operating system data instead of the locale encoding. Add ``-X utf8`` command line option and ``PYTHONUTF8`` environment variable. Context ======= Locale and operating system data -------------------------------- Python uses the ``LC_CTYPE`` locale to decide how to encode and decode data from/to the operating system: * file content * command line arguments: ``sys.argv`` * standard streams: ``sys.stdin``, ``sys.stdout``, ``sys.stderr`` * environment variables: ``os.environ`` * filenames: ``os.listdir(str)`` for example * pipes: ``subprocess.Popen`` using ``subprocess.PIPE`` for example * error messages * name of a timezone * user name, terminal name: ``os``, ``grp`` and ``pwd`` modules * host name, UNIX socket path: see the ``socket`` module * etc. At startup, Python calls ``setlocale(LC_CTYPE, "")`` to use the user ``LC_CTYPE`` locale and then store the locale encoding, ``sys.getfilesystemencoding()``. In the whole lifetime of a Python process, the same encoding and error handler are used to encode and decode data from/to the operating system. .. note:: In some corner case, the *current* ``LC_CTYPE`` locale must be used instead of ``sys.getfilesystemencoding()``. For example, the ``time`` module uses the *current* ``LC_CTYPE`` locale to decode timezone names. The POSIX locale and its encoding --------------------------------- The following environment variables are used to configure the locale, in this preference order: * ``LC_ALL``, most important variable * ``LC_CTYPE`` * ``LANG`` The POSIX locale,also known as "the C locale", is used: * if the first set variable is set to ``"C"`` * if all these variables are unset, for example when a program is started in an empty environment. The encoding of the POSIX locale must be ASCII or a superset of ASCII. On Linux, the POSIX locale uses the ASCII encoding. On FreeBSD and Solaris, ``nl_langinfo(CODESET)`` announces an alias of the ASCII encoding, whereas ``mbstowcs()`` and ``wcstombs()`` functions use the ISO 8859-1 encoding (Latin1) in practice. The problem is that ``os.fsencode()`` and ``os.fsdecode()`` use ``locale.getpreferredencoding()`` codec. For example, if command line arguments are decoded by ``mbstowcs()`` and encoded back by ``os.fsencode()``, an ``UnicodeEncodeError`` exception is raised instead of retrieving the original byte string. To fix this issue, Python now checks since Python 3.4 if ``mbstowcs()`` really uses the ASCII encoding if the the ``LC_CTYPE`` uses the the POSIX locale and ``nl_langinfo(CODESET)`` returns ``"ASCII"`` (or an alias to ASCII). If not (the effective encoding is not ASCII), Python uses its own ASCII codec instead of using ``mbstowcs()`` and ``wcstombs()`` functions for operating system data. See the `POSIX locale (2016 Edition) <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html>`_. C.UTF-8 and C.utf8 locales -------------------------- Some operating systems provide a variant of the POSIX locale using the UTF-8 encoding: * Fedora 25: ``"C.utf8"`` or ``"C.UTF-8"`` * Debian (eglibc 2.13-1, 2011): ``"C.UTF-8"`` * HP-UX: ``"C.utf8"`` It was proposed to add a ``C.UTF-8`` locale to glibc: `glibc C.UTF-8 proposal <https://sourceware.org/glibc/wiki/Proposals/C.UTF-8>`_. Popularity of the UTF-8 encoding -------------------------------- Python 3 uses UTF-8 by default for Python source files. On Mac OS X, Windows and Android, Python always use UTF-8 for operating system data instead of the locale encoding. For Windows, see the `PEP 529: Change Windows filesystem encoding to UTF-8 <https://www.python.org/dev/peps/pep-0529/>`_. On Linux, UTF-8 became the defacto standard encoding by default, replacing legacy encodings like ISO 8859-1 or ShiftJIS. For example, using different encodings for filenames and standard streams is likely to create mojibake, so UTF-8 is now used *everywhere*. The UTF-8 encoding is the default encoding of XML and JSON file format. In January 2017, UTF-8 was used in `more than 88% of web pages <https://w3techs.com/technologies/details/en-utf8/all/all>`_ (HTML, Javascript, CSS, etc.). See `utf8everywhere.org <http://utf8everywhere.org/>`_ for more general information on the UTF-8 codec. .. note:: Some applications and operating systems (especially Windows) use Byte Order Markers (BOM) to indicate the used Unicode encoding: UTF-7, UTF-8, UTF-16-LE, etc. BOM are not well supported and rarely used in Python. Old data stored in different encodings and surrogateescape ---------------------------------------------------------- Even if UTF-8 became the defacto standard, there are still systems in the wild which don't use UTF-8. And there are a lot of data stored in different encodings. For example, an old USB key using the ext3 filesystem with filenames encoded to ISO 8859-1. The Linux kernel and the libc don't decode filenames: a filename is used as a raw array of bytes. The common solution to support any filename is to store filenames as bytes and don't try to decode them. When displayed to stdout, mojibake is displayed if the filename and the terminal don't use the same encoding. Python 3 promotes Unicode everywhere including filenames. A solution to support filenames not decodable from the locale encoding was found: the ``surrogateescape`` error handler (`PEP 393 <https://www.python.org/dev/peps/pep-0393/>`_), store undecodable bytes as surrogate characters. This error handler is used by default for operating system data, by ``os.fsdecode()`` and ``os.fsencode()`` for example (except on Windows which uses the ``strict`` error handler). Standard streams ---------------- Python uses the locale encoding for standard streams: stdin, stdout and stderr. The ``strict`` error handler is used by stdin and stdout to prevent mojibake. The ``backslashreplace`` error handler is used by stderr to avoid Unicode encode error when displaying non-ASCII text. It is especially useful when the POSIX locale is used, because this locale usually uses the ASCII encoding. The problem is that operating system data like filenames are decoded using the ``surrogateescape`` error handler (PEP 393). Displaying a filename to stdout raises an Unicode encode error if the filename contains an undecoded byte stored as a surrogate character. Python 3.6 now uses ``surrogateescape`` for stdin and stdout if the POSIX locale is used: `issue #19977 <http://bugs.python.org/issue19977>`_. The idea is to passthrough operating system data even if it means mojibake, because most UNIX applications work like that. Most UNIX applications store filenames as bytes, usually simply because bytes are first-citizen class in the used programming language, whereas Unicode is badly supported. .. note:: The encoding and/or the error handler of standard streams can be overriden with the ``PYTHONIOENCODING`` environment variable. Proposal ======== Add a new UTF-8 mode, opt-in option to use UTF-8 for operating system data instead of the locale encoding: * Add ``-X utf8`` command line option * Add ``PYTHONUTF8=1`` environment variable Add also a strict UTF-8 mode, enabled by ``-X utf8=strict`` or ``PYTHONUTF8=strict``. The UTF-8 mode changes the default encoding and error handler used by open(), os.fsdecode(), os.fsencode(), sys.stdin, sys.stdout and sys.stderr: ============================ ======================= ======================= ====================== ====================== Function Default, other locales Default, POSIX locale UTF-8 UTF-8 Strict ============================ ======================= ======================= ====================== ====================== open() locale/strict locale/strict UTF-8/surrogateescape UTF-8/strict os.fsdecode(), os.fsencode() locale/surrogateescape locale/surrogateescape UTF-8/surrogateescape UTF-8/strict sys.stdin locale/strict locale/surrogateescape UTF-8/surrogateescape UTF-8/strict sys.stdout locale/strict locale/surrogateescape UTF-8/surrogateescape UTF-8/strict sys.stderr locale/backslashreplace locale/backslashreplace UTF-8/backslashreplace UTF-8/backslashreplace ============================ ======================= ======================= ====================== ====================== The UTF-8 mode is disabled by default to keep hard Unicode errors when encoding or decoding operating system data failed, and to keep the backward compatibility. The user is responsible to enable explicitly the UTF-8 mode, and so is better prepared for mojibake than if the UTF-8 mode would be enabled *by default*. The UTF-8 mode should be used on systems known to be configured with UTF-8 where most applications speak UTF-8. It prevents Unicode errors if the user overrides a locale *by mistake* or if a Python program is started with no locale configured (and so with the POSIX locale). Most UNIX applications handle operating system data as bytes, so ``LC_ALL``, ``LC_CTYPE`` and ``LANG`` environment variables have a limited impact on how these data are handled by the application. The Python UTF-8 mode should help to make Python more interoperable with the other UNIX applications in the system assuming that *UTF-8* is used everywhere and that users *expect* UTF-8. Ignoring ``LC_ALL``, ``LC_CTYPE`` and ``LANG`` environment variables in Python is more convenient, since they are more commonly misconfigured *by mistake* (configured to use an encoding different than UTF-8, whereas the system uses UTF-8), rather than being misconfigured by intent. Backward Compatibility ====================== Since the UTF-8 mode is disabled by default, it has no impact on the backward compatibility. The new UTF-8 mode must be enabled explicitly. Alternatives ============ Always use UTF-8 ---------------- Python already always use the UTF-8 encoding on Mac OS X, Android and Windows. Since UTF-8 became the defacto encoding, it makes sense to always use it on all platforms with any locale. The risk is to introduce mojibake if the locale uses a different encoding, especially for locales other than the POSIX locale. Force UTF-8 for the POSIX locale -------------------------------- An alternative to always using UTF-8 in any case is to only use UTF-8 when the ``LC_CTYPE`` locale is the POSIX locale. The `PEP 538: Coercing the legacy C locale to C.UTF-8 <https://www.python.org/dev/peps/pep-0538/>`_ of Nick Coghlan proposes to implement that using the ``C.UTF-8`` locale. Related Work ============ Perl has a ``-C`` command line option and a ``PERLUNICODE`` environment varaible to force UTF-8: see `perlrun <http://perldoc.perl.org/perlrun.html>`_. It is possible to configure UTF-8 per standard stream, on input and output streams, etc. Copyright ========= This document has been placed in the public domain. [View Less]

14 58

Re: [Python-ideas] Settable defaulting to decimal instead of float
by George Fischhof Jan. 12, 2017

Jan. 12, 2017

2017-01-12 13:13 GMT+01:00 Stephan Houben <stephanh42(a)gmail.com>: > Something like: > > from __syntax__ import decimal_literal > > which would feed the rest of the file through the "decimal_literal" > transpiler. > (and not influence anything in other files). > > Not sure if you would want to support multiple transpilers per file. > > Note that Racket has something similar with their initial "#lang ..." > directive. > That only allows a single "… [View More]language". Possibly wisely so. > > Stephan > > > 2017-01-12 12:59 GMT+01:00 אלעזר <elazarg(a)gmail.com>: > >> I think such proposals are special cases of a general theme: a compiler >> pragma, similar to "from __future__", to make Python support >> domain-specific syntax in the current file. Whether it's decimal literals >> or matrix/vector literals etc. >> >> I think it will be nice to make some tool, external to Python, that will >> allow defining such "sibling languages" (transpiled into Python) easily and >> uniformly. >> >> Elazar >> >> בתאריך יום ה׳, 12 בינו' 2017, 13:21, מאת Paul Moore ‏<p.f.moore(a)gmail.com >> >: >> >>> On 12 January 2017 at 10:28, Victor Stinner <victor.stinner(a)gmail.com> >>> wrote: >>> > George requested this feature on the bug tracker: >>> > http://bugs.python.org/issue29223 >>> > >>> > George was asked to start a discusson on this list. I posted the >>> > following comment before closing the issue: >>> > >>> > You are not the first one to propose the idea. >>> >>> OK, but without additional detail (for example, how would the proposed >>> flag work, if the main module imports module A, then would float >>> literals in A be decimal or binary? Both could be what the user wants) >>> it's hard to comment. And as you say, most of this has been discussed >>> before, so I'd like to see references back to the previous discussions >>> in any proposal, with explanations of how the new proposal addresses >>> the objections raised previously. >>> >>> Paul >> >> Most of the time one of my students talks to me about decimal vs > binary, they're thinking that a decimal literal (or converting the > default non-integer literal to be decimal) is a panacea to the "0.1 + > 0.2 != 0.3" problem. Perhaps the real solution is a written-up > explanation of why binary floating point is actually a good thing, and > not just a backward-compatibility requirement? > > ChrisA from __future__ import use_decimal_instead_of_float or any other import would be very good. The most important thing in my point of view is that I do not want to convert every variable every time to decimal. Accuracy is important for me (yes, 0.1 + 0.2 should equal to 0.3 , no more, no less ;-) ) And if it is mentioned, I would like to ask why binary floating point is "better". It is faster, I agree, but why "better"? Actually I create test automation (I am a senior QA eng), the fastest test case runs for about 1-2 minutes. I do not know the exact time difference between binary and decimal arithmetic, but I do not care with this. My test would run some microseconds faster. It does not matter at a minute range. In the tests I calculate with numbers with 4 decimal digits, and I need exact match. ;-) Actually I have a new colleague, they did image analysis, and the calculated much calculations, and they used a library (not python) that is accurate as well. Becasue accuracy was more important for them as well. BR George [View Less]

3 3

How to respond to trolling
by Guido van Rossum Jan. 12, 2017

Jan. 12, 2017

Was it really necessary for all the usual folks on this list to engage with the "Python review" threads? I think a much more effective response would have been a resounding silence. -- --Guido van Rossum (python.org/~guido)

11 12

api suggestions for the cProfile module
by Thane Brimhall Jan. 11, 2017

Jan. 11, 2017

I use cProfile a lot, and would like to suggest three backwards-compatible improvements to the API. 1: When using cProfile on a specific piece of code I often use the enable() and disable() methods. It occurred to me that this would be an obvious place to use a context manager. 2: Enhance the `print_stats` method on Profile to accept more options currently available only through the pstats.Stats class. For example, strip_dirs could be a boolean argument, and limit could accept an int. This … [View More]

5 6

Re: [Python-ideas] Python reviewed
by Simon Lovell Jan. 11, 2017

Jan. 11, 2017

Oh one last thing (I hope), the argument for having the current slice notation by Dijkstra, that it looks messy to have a loop where the contents are never executed or can no longer be executed is ridiculous! That *should* look messy. for range(1,1): means executing once to me. If you had 1 based, two of four of the other idioms would work the same: s[:n] + s[n:] == s // doesn't work. I don't think it should work though len(s[:n]) == n // works len(s[:-n]) == n // rather … [View More]

2 1

api suggestions for the cProfile module
by Jelle Zijlstra Jan. 10, 2017

Jan. 10, 2017

2017-01-10 8:57 GMT-08:00 Ethan Furman <ethan(a)stoneleaf.us>: > On 01/10/2017 08:36 AM, Thane Brimhall wrote: > > Does anyone have thoughts on this topic? I assume the silence is because >> this suggestion is too trivial to matter. >> > > Sometimes it's just a matter of timing. :) > > I use cProfile a lot, and would like to suggest three backwards-compatible >> improvements to the API. >> >> 1: When using cProfile on a specific piece … [View More]of code I often use the >> enable() and disable() methods. It occurred to me that this would >> be an obvious place to use a context manager. >> > > Absolutely. > > 2: Enhance the `print_stats` method on Profile to accept more options >> currently available only through the pstats.Stats class. For example, >> strip_dirs could be a boolean argument, and limit could accept an int. >> This would reduce the number of cases you'd need to use the more complex >> API. >> > > I don't have much experience with cProfile, but this seems reasonable. > > 3: I often forget which string keys are available for sorting. It would >> be nice to add an enum for these so a user could have their linter and >> IDE check that value pre-runtime. Since it would subclass `str` and >> `Enum` it would still work with all currently existing code. >> > > Absolutely! :) > > The current documentation contains the following code: >> >> import cProfile, pstats, io >> pr = cProfile.Profile() >> pr.enable() >> # ... do something ... >> pr.disable() >> s = io.StringIO() >> sortby = 'cumulative' >> ps = pstats.Stats(pr, stream=s).sort_stats(sortby) >> ps.print_stats() >> print(s.getvalue()) >> >> While the code below doesn't exactly match the functionality above (eg. >> not >> using StringIO), I envision the context manager working like this, along >> with some adjustments on how to get the stats from the profiler: >> >> import cProfile, pstats >> with cProfile.Profile() as pr: >> # ... do something ... >> pr.print_stats(sort=pstats.Sort.cumulative, limit=10, >> strip_dirs=True) >> >> As you can see, the code is shorter and somewhat more self-documenting. >> The >> best thing about these suggestions is that as far as I can tell they >> would >> be backwards-compatible API additions. >> > > The `pr.print_stats... line should not be inside the `with` block unless > you want to profile that part as well. > > These suggestions seem fairly uncontroversial. Have you opened an issue > on the issue tracker? > > The fun part of the patch will be the C code, but a Python > proof-of-concept would be useful. > > These changes may not even require C code, since (contrary to its name) cProfile actually is implemented partly in Python. For example, the context manager change could be made simply by adding __enter__ and __exit__ to the cProfile.Profile class. > -- > ~Ethan~ > _______________________________________________ > Python-ideas mailing list > Python-ideas(a)python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > [View Less]

2 1

Re: [Python-ideas] Python Reviewed
by Simon Lovell Jan. 10, 2017

Jan. 10, 2017

Hi Kyle, I don't see the harm caused from having a do-while construct. Not the most used construct but it is sometimes useful and not having it means you need to either have a first time through marker or a break at the end of a "while True:" loop. I would say that None should also be non-boolean. Otherwise you are saying that things which might be None would be True if not None. Re: SQLAlchemy, this does not resolve the issues satisfactorily to me. Re: half-loop. The idea that you … [View More]

4 3

Re: [Python-ideas] Python reviewed
by Simon Lovell Jan. 10, 2017

Jan. 10, 2017

Thanks for the feedback guys. A few quick comments: Re: Colons. I'm sure I've seen that FAQ before. I may be arrogant but I can't take it seriously. Being "slightly" easier to read is hardly a reason for a mandatory structure. Re: PEP249. I thought I'd detailed quite a bit of what I thought should be possible. Is there a forum for advancing this? Re: do-while - that a is a loop construct that executes once before evaluating the condition. Supported by most languages. Re: Counters … [View More]

7 7