Re: Python 3.2 has some deadly infection

From	Akira Li <4kir4.1i@gmail.com>
Subject	Re: Python 3.2 has some deadly infection
Date	2014-06-06 12:03 +0400
References	(15 earlier) <87wqcvu20h.fsf@elektro.pacujo.net> <7b3543f6-6f62-49c5-abdc-e2783fd6d629@googlegroups.com> <87oay7tnxt.fsf@elektro.pacujo.net> <53908dd0$0$29978$c3e8da3$5496439d@news.astraweb.com> <87ha3zti2h.fsf@elektro.pacujo.net>
Newsgroups	comp.lang.python
Message-ID	<mailman.10807.1402041845.18130.python-list@python.org> (permalink)

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Marko Rauhamaa <marko@pacujo.net> writes:

> Steven D'Aprano <steve+comp.lang.python@pearwood.info>:
>
>> Nevertheless, there are important abstractions that are written on top
>> of the bytes layer, and in the Unix and Linux world, the most
>> important abstraction is *text*. In the Unix world, text formats and
>> text processing is much more common in user-space apps than binary
>> processing.
>
> That linux text is not the same thing as Python's text. Conceptually,
> Python text is a sequence of 32-bit integers. Linux text is a sequence
> of 8-bit integers.

_Unicode string in Python is a sequence of Unicode codepoints_. It is
correct that 32-bit integer is enough to represent any Unicode
codepoint: \u0000...\U0010FFFF 

It says *nothing* about how Unicode strings are represented
*internally* in Python. It may vary from version to version, build
options and even may depend on the content of a string at runtime.

In the past, "narrow builds" might break the abstraction in some cases
that is why Linux distributions used wide python builds.

_Unicode codepoint is  not a Python concept_. There is Unicode
standard http://unicode.org Though intead of following the
self-referential defenitions web, I find it easier to learn from
examples such as http://codepoints.net/U+0041 (A) or
http://codepoints.net/U+1F3A7 (🎧)

_There is no such thing as 8-bit text_
http://www.joelonsoftware.com/articles/Unicode.html

If you insert a space after each byte (8-bit) in the input text then you
may get garbage i.e., you can't assume that a character is a byte:

  $ echo "Hyvää yötä" | perl -pe's/.\K/ /g'
  H y v a � � � �   y � � t � �

In general, you can't assume that a character is a Unicode codepoint:

  $ echo "Hyvää yötä" | perl -C -pe's/.\K/ /g'
  H y v a ̈ ä   y ö t ä

The eXtended grapheme clusters (user-perceived characters) may be useful
in this case:

  $ echo "Hyvää yötä" | perl -C -pe's/\X\K/ /g'
  H y v ä ä   y ö t ä

\X pattern is supported by `regex` module in Python i.e., you can't even
iterate over characters (as they are seen by a user) in Python using
only stdlib. \w+ pattern is also broken for Unicode text
http://bugs.python.org/issue1693050 (it is fixed in the `regex` module)
i.e., you can't select a word in Unicode text using only stdlib.

\X along is not enough in some cases e.g., "“ch” may be considered a
grapheme cluster in Slovak, for processes such as collation" [1]
(sorting order). `PyICU` module might be useful here.

Knowing about Unicode normalization forms (NFC, NFKD, etc)
http://unicode.org/reports/tr15/ Unicode
text segmentation [1] and Unicode collation algorithm
http://www.unicode.org/reports/tr10/ concepts is also 
useful; if you want to work with text. 

[1]: http://www.unicode.org/reports/tr29/

--
akira

Thread

Python 3.2 has some deadly infection Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-31 17:10 +0100
  Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-05-31 22:55 +0300
  Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-01 02:26 +0000
    Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-01 12:43 +1000
    Re: Python 3.2 has some deadly infection Tim Delaney <timothy.c.delaney@gmail.com> - 2014-06-02 08:54 +1000
      Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-02 01:14 +0000
        Re: Python 3.2 has some deadly infection Tim Delaney <timothy.c.delaney@gmail.com> - 2014-06-02 12:23 +1000
          Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-01 19:46 -0700
        Re: Python 3.2 has some deadly infection Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2014-06-02 07:45 +0000
        Re: Python 3.2 has some deadly infection Tim Delaney <timothy.c.delaney@gmail.com> - 2014-06-02 19:02 +1000
        Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-02 19:14 +1000
        Re: Python 3.2 has some deadly infection Robin Becker <robin@reportlab.com> - 2014-06-02 12:10 +0100
          Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-03 16:34 +0000
            Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-04 02:43 +1000
        Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-02 17:34 -0400
          Re: Python 3.2 has some deadly infection Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-06-03 17:16 +1200
            Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-03 02:21 -0400
            Re: Python 3.2 has some deadly infection Robin Becker <robin@reportlab.com> - 2014-06-03 15:18 +0100
              Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-04 13:08 +0000
                Re: Python 3.2 has some deadly infection Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-06-05 14:01 +1200
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 10:16 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-05 17:30 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 11:05 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-05 18:36 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 12:53 +0300
                Re: Python 3.2 has some deadly infection wxjmfauth@gmail.com - 2014-06-05 05:43 -0700
                Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-05 14:50 -0400
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 23:21 +0300
                Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-05 18:09 -0400
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-05 23:13 +0000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 02:30 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 09:39 +1000
                Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-05 22:08 -0400
                Re: Python 3.2 has some deadly infection Ethan Furman <ethan@stoneleaf.us> - 2014-06-05 20:47 -0700
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve@pearwood.info> - 2014-06-05 08:34 +0000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 12:41 +0300
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-05 06:37 -0700
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 17:45 +0300
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-05 15:33 +0000
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 02:12 +1000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-05 09:54 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 03:36 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 19:52 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 03:28 +1000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-05 15:35 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 08:52 +1000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-05 20:11 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 13:20 +1000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-05 20:32 -0700
                Re: Python 3.2 has some deadly infection Akira Li <4kir4.1i@gmail.com> - 2014-06-06 12:03 +0400
                Re: Python 3.2 has some deadly infection Robin Becker <robin@reportlab.com> - 2014-06-05 16:37 +0100
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-05 16:16 +0000
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 01:50 +1000
                Re: Python 3.2 has some deadly infection Robin Becker <robin@reportlab.com> - 2014-06-05 17:17 +0100
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-05 16:32 +0000
                Re: Python 3.2 has some deadly infection Ethan Furman <ethan@stoneleaf.us> - 2014-06-06 07:40 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-06 03:14 +1000
                Re: Python 3.2 has some deadly infection Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-05 11:16 -0600
                Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-05 14:11 -0400
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-05 21:30 +0300
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-05 23:02 +0000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 02:21 +0300
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-06 12:15 +0000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 16:00 +0300
                Re: Python 3.2 has some deadly infection rurpy@yahoo.com - 2014-06-07 21:34 -0700
                Re: Python 3.2 has some deadly infection Ethan Furman <ethan@stoneleaf.us> - 2014-06-06 06:24 -0700
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 17:10 +0300
                Re: Python 3.2 has some deadly infection Michael Torrie <torriem@gmail.com> - 2014-06-06 09:02 -0600
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 18:32 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 01:50 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 20:02 +0300
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-06 10:13 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 03:26 +1000
                Re: Python 3.2 has some deadly infection wxjmfauth@gmail.com - 2014-06-06 11:03 -0700
                Re: Python 3.2 has some deadly infection Denis McMahon <denismfmcmahon@gmail.com> - 2014-06-06 21:18 +0000
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 08:18 +1000
                Re: Python 3.2 has some deadly infection Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-06 15:57 +0000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-06 09:21 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 02:48 +1000
                Re: Python 3.2 has some deadly infection Rustom Mody <rustompmody@gmail.com> - 2014-06-06 10:04 -0700
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 03:12 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 20:11 +0300
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 03:16 +1000
                Re: Python 3.2 has some deadly infection Marko Rauhamaa <marko@pacujo.net> - 2014-06-06 20:18 +0300
                Re: Python 3.2 has some deadly infection Ned Batchelder <ned@nedbatchelder.com> - 2014-06-06 13:33 -0400
                Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-07 01:25 +1000
                Re: Python 3.2 has some deadly infection wxjmfauth@gmail.com - 2014-06-06 08:44 -0700
                Re: Python 3.2 has some deadly infection wxjmfauth@gmail.com - 2014-06-06 08:48 -0700
                Re: Python 3.2 has some deadly infection Robin Becker <robin@reportlab.com> - 2014-06-06 12:56 +0100
                Re: Python 3.2 has some deadly infection Akira Li <4kir4.1i@gmail.com> - 2014-06-05 06:49 +0400
            Re: Python 3.2 has some deadly infection Chris Angelico <rosuav@gmail.com> - 2014-06-04 00:25 +1000
            Re: Python 3.2 has some deadly infection Terry Reedy <tjreedy@udel.edu> - 2014-06-03 14:22 -0400

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