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Could you verify this, Oh Great Unicode Experts of the Python-List?

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  Could you verify this, Oh Great Unicode Experts of the Python-List? Joshua Landau <joshua@landau.ws> - 2013-08-11 07:17 +0100
    Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-11 09:09 +0000
      Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Joshua Landau <joshua@landau.ws> - 2013-08-11 10:44 +0100
        Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-11 11:14 +0000
          Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Chris Angelico <rosuav@gmail.com> - 2013-08-11 12:45 +0100
          Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Joshua Landau <joshua@landau.ws> - 2013-08-11 12:59 +0100
          Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Joshua Landau <joshua@landau.ws> - 2013-08-13 09:40 +0100
      Re: Could you verify this, Oh Great Unicode Experts of the Python-List? wxjmfauth@gmail.com - 2013-08-11 05:51 -0700
        Re: Could you verify this, Oh Great Unicode Experts of the Python-List? Joshua Landau <joshua@landau.ws> - 2013-08-11 14:07 +0100

#52362 — Could you verify this, Oh Great Unicode Experts of the Python-List?

Basically, I think Twitter's broken.

For my full discusion on the matter, see:
http://www.reddit.com/r/learnpython/comments/1k2yrn/help_with_len_and_input_function_33/cbku5e8

Here's the first post of mine, ineffectually edited for this list:

"""
<strikethrough>The obvious solution [to getting the length of a tweet]
is wrong. Like, slightly wrong¹.</strikethrough>

Given tweet = b"caf\x65\xCC\x81".decode():

    >>> tweet
    'café'

But:

    >>> len(tweet)
    5

So the solution is:

    >>> import unicodedata
    >>> len(unicodedata.normalize("NFC", tweet))
    4

<strikethrough>Read twitter's commentary¹ for proof.</strikethrough>

<strikethrough>There are additional complications I'm trying to sort
out.</strikethrough>
________________________________

After further testing (I don't actually use Twitter) it seems the
whole thing was just smoke and mirrors. The linked article is a lie,
at least on the user's end.

On Linux you can prove this by running:

    >>> p = subprocess.Popen(['xsel', '-bi'], stdin=subprocess.PIPE)
    >>> p.communicate(input=b"caf\x65\xCC\x81")
    (None, None)

"café" will be in your Copy-Paste buffer, and you can paste it in to
the tweet-box. It takes 5 characters. So much for testing ;).

________________________________
¹ https://dev.twitter.com/docs/counting-characters#Definition_of_a_Character
"""


I know this isn't *really* Python-related, but there's Python involved
and you're the sort of people who'll be able to tell me what I've done
wrong, if anything.

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#52373

On Sun, 11 Aug 2013 07:17:42 +0100, Joshua Landau wrote:

> Basically, I think Twitter's broken.

Oh, in about a million ways, but apparently people like it :-(


> For my full discusion on the matter, see:
> http://www.reddit.com/r/learnpython/comments/1k2yrn/
help_with_len_and_input_function_33/cbku5e8
> 
> Here's the first post of mine, ineffectually edited for this list:
> 
> """
> <strikethrough>The obvious solution [to getting the length of a tweet]
> is wrong. Like, slightly wrong¹.</strikethrough>
> 
> Given tweet = b"caf\x65\xCC\x81".decode():

I assume you're using Python 3, where UTF-8 is the default encoding.


>     >>> tweet
>     'café'
> 
> But:
> 
>     >>> len(tweet)
>     5

Yes, that's correct. Unicode doesn't promise to have a single unique 
representation for all human-readable strings. In this case, the string 
"cafe" with an accent on the "e" can be generated by two sequences of 
code points:

LATIN SMALL LETTER C
LATIN SMALL LETTER A
LATIN SMALL LETTER F
LATIN SMALL LETTER E
COMBINING ACUTE ACCENT

or 

LATIN SMALL LETTER C
LATIN SMALL LETTER A
LATIN SMALL LETTER F
LATIN SMALL LETTER E WITH ACUTE


The reason some accented letters have single code point forms is to 
support legacy charsets; the reason some only exist as combining 
characters is due to the combinational explosion. Some languages allow 
you to add up to five or six different accent on any of dozens of 
different letters. If each combination needed its own unique code point, 
there wouldn't be enough code points. For bonus points, if there are five 
accents that can be placed in any combination of zero or more on any of 
four characters, how many code points would be needed?

Neither form is "right" or "wrong", they are both equally valid. They 
encode differently, of course, since UTF-8 does guarantee that every 
sequence of code points has a unique byte representation:

py> tweet.encode('utf-8')
'cafe\xcc\x81'
py> u'café'.encode('utf-8')
'caf\xc3\xa9'

Note that the form you used, b"caf\x65\xCC\x81", is the same as the first 
except that you have shown "e" in hex for some reason:

py> b'\x65' == b'e'
True


> So the solution is:
> 
>     >>> import unicodedata
>     >>> len(unicodedata.normalize("NFC", tweet))
>     4

In this particular case, this will reduce the tweet to the normalised 
form that Twitter uses.


[...]
> After further testing (I don't actually use Twitter) it seems the whole
> thing was just smoke and mirrors. The linked article is a lie, at least
> on the user's end.

Which linked article? The one on dev.twitter.com seems to be okay to me. 
Of course, they might be lying when they say "Twitter counts the length 
of a Tweet using the Normalization Form C (NFC) version of the text", I 
have no idea. But the seem to have a good grasp of the issues involved, 
and assuming they do what they say, at least Western European users 
should be happy.


> On Linux you can prove this by running:
> 
>     >>> p = subprocess.Popen(['xsel', '-bi'], stdin=subprocess.PIPE)
>     >>> p.communicate(input=b"caf\x65\xCC\x81")
>     (None, None)
> 
> "café" will be in your Copy-Paste buffer, and you can paste it in to
> the tweet-box. It takes 5 characters. So much for testing ;).

How do you know that it takes 5 characters? Is that some Javascript 
widget? I'd blame buggy Javascript before Twitter.

If this shows up in your application as café rather than café, it is a 
bug in the text rendering engine. Some applications do not deal with 
combining characters correctly.

(It's a hard problem to solve, and really needs support from the font. In 
some languages, the same accent will appear in different places depending 
on the character they are attached to, or the other accents there as 
well. Or so I've been lead to believe.)


> ¹ https://dev.twitter.com/docs/counting-
> characters#Definition_of_a_Character

Looks reasonable to me. No obvious errors to my eyes.


-- 
Steven

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#52375

On 11 August 2013 10:09, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> The reason some accented letters have single code point forms is to
> support legacy charsets; the reason some only exist as combining
> characters is due to the combinational explosion. Some languages allow
> you to add up to five or six different accent on any of dozens of
> different letters. If each combination needed its own unique code point,
> there wouldn't be enough code points. For bonus points, if there are five
> accents that can be placed in any combination of zero or more on any of
> four characters, how many code points would be needed?

52?

> Note that the form you used, b"caf\x65\xCC\x81", is the same as the first
> except that you have shown "e" in hex for some reason:
>
> py> b'\x65' == b'e'
> True

Yeah.. I did that because the linked post did it. I'm not sure why either ;).

> On Sun, 11 Aug 2013 07:17:42 +0100, Joshua Landau wrote:
>>
>> So the solution is:
>>
>>     >>> import unicodedata
>>     >>> len(unicodedata.normalize("NFC", tweet))
>>     4
>
> In this particular case, this will reduce the tweet to the normalised
> form that Twitter uses.
>
> [...]
>> After further testing (I don't actually use Twitter) it seems the whole
>> thing was just smoke and mirrors. The linked article is a lie, at least
>> on the user's end.
>
> Which linked article? The one on dev.twitter.com seems to be okay to me.

That's the one.

> Of course, they might be lying when they say "Twitter counts the length
> of a Tweet using the Normalization Form C (NFC) version of the text", I
> have no idea. But the seem to have a good grasp of the issues involved,
> and assuming they do what they say, at least Western European users
> should be happy.

They *don't* seem to be doing what they say.

>> On Linux you can prove this by running:
>>
>>     >>> p = subprocess.Popen(['xsel', '-bi'], stdin=subprocess.PIPE)
>>     >>> p.communicate(input=b"caf\x65\xCC\x81")
>>     (None, None)
>>
>> "café" will be in your Copy-Paste buffer, and you can paste it in to
>> the tweet-box. It takes 5 characters. So much for testing ;).
>
> How do you know that it takes 5 characters? Is that some Javascript
> widget? I'd blame buggy Javascript before Twitter.

I go to twitter.com, log in and press that odd blue compose button in
the top-right. After pasting at says I have 135 (down from 140)
characters left.

My only question here is, since you can't post after 140
non-normalised characters, who cares if the server counts it as less?

> If this shows up in your application as café rather than café, it is a
> bug in the text rendering engine. Some applications do not deal with
> combining characters correctly.

Why the rendering engine?

> (It's a hard problem to solve, and really needs support from the font. In
> some languages, the same accent will appear in different places depending
> on the character they are attached to, or the other accents there as
> well. Or so I've been lead to believe.)
>
>
>> ¹ https://dev.twitter.com/docs/counting-
>> characters#Definition_of_a_Character
>
> Looks reasonable to me. No obvious errors to my eyes.

*Not sure whether talking about the link or my post*

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#52379

On Sun, 11 Aug 2013 10:44:40 +0100, Joshua Landau wrote:

> On 11 August 2013 10:09, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
>> The reason some accented letters have single code point forms is to
>> support legacy charsets; the reason some only exist as combining
>> characters is due to the combinational explosion. Some languages allow
>> you to add up to five or six different accent on any of dozens of
>> different letters. If each combination needed its own unique code
>> point, there wouldn't be enough code points. For bonus points, if there
>> are five accents that can be placed in any combination of zero or more
>> on any of four characters, how many code points would be needed?
> 
> 52?

More than double that.

Consider a single character. It can have 0 to 5 accents, in any 
combination. Order doesn't matter, and there are no duplicates, so there 
are:

0 accent: take 0 from 5 = 1 combination;
1 accent: take 1 from 5 = 5 combinations;
2 accents: take 2 from 5 = 5!/(2!*3!) = 10 combinations;
3 accents: take 3 from 5 = 5!/(3!*2!) = 10 combinations;
4 accents: take 4 from 5 = 5 combinations;
5 accents: take 5 from 5 = 1 combination

giving a total of 32 combinations for a single character. Since there are 
four characters in this hypothetical language that take accents, that 
gives a total of 4*32 = 128 distinct code points needed.

In reality, Unicode has currently code points U+0300 to U+036F (112 code 
points) to combining characters. It's not really meaningful to combine 
all 112 of them, or even most of 112 of them, but let's assume that we 
can legitimately combine up to three of them on average (some languages 
will allow more, some less) on just six different letters. That gives us:

0 accent: 1 combination
1 accent: 112 combinations
2 accents: 112!/(2!*110!) = 6216 combinations
3 accents: 112!/(3!*109!) = 227920 combinations

giving 234249 combinations, by six base characters, = 1405494 code 
points. Which is comfortably more than the 1114112 code points Unicode 
has in total :-)

This calculation is horribly inaccurate, since you can't arbitrarily 
combine (say) accents from Greek with accents from IPA, but I reckon that 
the combinational explosion of accented letters is still real.


[...]
>> Of course, they might be lying when they say "Twitter counts the length
>> of a Tweet using the Normalization Form C (NFC) version of the text", I
>> have no idea. But the seem to have a good grasp of the issues involved,
>> and assuming they do what they say, at least Western European users
>> should be happy.
> 
> They *don't* seem to be doing what they say.
[...]
>>> "café" will be in your Copy-Paste buffer, and you can paste it in to
>>> the tweet-box. It takes 5 characters. So much for testing ;).
>>
>> How do you know that it takes 5 characters? Is that some Javascript
>> widget? I'd blame buggy Javascript before Twitter.
> 
> I go to twitter.com, log in and press that odd blue compose button in
> the top-right. After pasting at says I have 135 (down from 140)
> characters left.

I'm pretty sure that will be a piece of Javascript running in your 
browser that reports the number of characters in the text box. So, I 
would expect that either:

- Javascript doesn't provide a way to normalize text;

- Twitter's Javascript developer(s) don't know how to normalize text, or 
can't be bothered to follow company policy (shame on them);

- the Javascript just asks the browser, and the browser doesn't know how 
to count characters the Twitter way;

etc. But of course posting to Twitter via your browser isn't the only way 
to post. Twitter provide an API to twit, and *that* is the ultimate test 
of whether Twitter's dev guide is lying or not.


> My only question here is, since you can't post after 140 non-normalised
> characters, who cares if the server counts it as less?

People who bypass the browser and write their own Twitter client.


>> If this shows up in your application as café rather than café, it is a
>> bug in the text rendering engine. Some applications do not deal with
>> combining characters correctly.
> 
> Why the rendering engine?

If the text renderer assumes it can draw once code point at a time, it 
will draw the "e", then reach the combining accent. It could, in 
principle, backspace and draw it over the "e", but more likely it will 
just draw it next to it.

What the renderer should do is walk the string, collecting characters 
until it reaches one which is not a combining character, then draw them 
all at once one on top of each other. A good font may have special 
glyphs, or at least hints, for combining accents. For instance, if you 
have a dot accent and a comma accent drawn one on top of the other, it 
looks like a comma; what you are supposed to do is move them side by 
side, so you have separate dot and comma glyphs.


>> (It's a hard problem to solve, and really needs support from the font.
>> In some languages, the same accent will appear in different places
>> depending on the character they are attached to, or the other accents
>> there as well. Or so I've been lead to believe.)
>>
>>
>>> ¹ https://dev.twitter.com/docs/counting-
>>> characters#Definition_of_a_Character
>>
>> Looks reasonable to me. No obvious errors to my eyes.
> 
> *Not sure whether talking about the link or my post*

The dev.twitter.com post.



-- 
Steven

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#52380

On Sun, Aug 11, 2013 at 12:14 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Consider a single character. It can have 0 to 5 accents, in any
> combination. Order doesn't matter, and there are no duplicates, so there
> are:
>
> 0 accent: take 0 from 5 = 1 combination;
> 1 accent: take 1 from 5 = 5 combinations;
> 2 accents: take 2 from 5 = 5!/(2!*3!) = 10 combinations;
> 3 accents: take 3 from 5 = 5!/(3!*2!) = 10 combinations;
> 4 accents: take 4 from 5 = 5 combinations;
> 5 accents: take 5 from 5 = 1 combination
>
> giving a total of 32 combinations for a single character. Since there are
> four characters in this hypothetical language that take accents, that
> gives a total of 4*32 = 128 distinct code points needed.

There's an easy way to calculate it. Instead of the "take N from 5"
notation, simply look at it as a set of independent bits - each of
your accents may be either present or absent. So it's 1<<5
combinations for a single character, which is the same 32 figure you
came up with, but easier to work with in the ridiculous case.

> In reality, Unicode has currently code points U+0300 to U+036F (112 code
> points) to combining characters. It's not really meaningful to combine
> all 112 of them, or even most of 112 of them...

If you *were* to use literally ANY combination, that would be 1<<112
which is... uhh... five billion yottacombinations. Don't bother
working that one out by the "take N" method, it'll take you too long
:)

Oh, and that's 1<<112 possible combining character combinations, so
you then need to multiply that by the number of base characters you
could use....

ChrisA

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#52382

On 11 August 2013 12:14, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Sun, 11 Aug 2013 10:44:40 +0100, Joshua Landau wrote:
>
>> On 11 August 2013 10:09, Steven D'Aprano
>> <steve+comp.lang.python@pearwood.info> wrote:
>>> The reason some accented letters have single code point forms is to
>>> support legacy charsets; the reason some only exist as combining
>>> characters is due to the combinational explosion. Some languages allow
>>> you to add up to five or six different accent on any of dozens of
>>> different letters. If each combination needed its own unique code
>>> point, there wouldn't be enough code points. For bonus points, if there
>>> are five accents that can be placed in any combination of zero or more
>>> on any of four characters, how many code points would be needed?
>>
>> 52?
>
> More than double that.
>
> Consider a single character. It can have 0 to 5 accents, in any
> combination. Order doesn't matter, and there are no duplicates, so there
> are:
>
> 0 accent: take 0 from 5 = 1 combination;
> 1 accent: take 1 from 5 = 5 combinations;
> 2 accents: take 2 from 5 = 5!/(2!*3!) = 10 combinations;
> 3 accents: take 3 from 5 = 5!/(3!*2!) = 10 combinations;
> 4 accents: take 4 from 5 = 5 combinations;
> 5 accents: take 5 from 5 = 1 combination
>
> giving a total of 32 combinations for a single character. Since there are
> four characters in this hypothetical language that take accents, that
> gives a total of 4*32 = 128 distinct code points needed.

I didn't see "four characters", and I did (1 + 5 + 10) * 2 and came up
with 52...
Maybe I should get more sleep.

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#52447

On 11 August 2013 12:14, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Sun, 11 Aug 2013 10:44:40 +0100, Joshua Landau wrote:
>>>> "café" will be in your Copy-Paste buffer, and you can paste it in to
>>>> the tweet-box. It takes 5 characters. So much for testing ;).
>>>
>>> How do you know that it takes 5 characters? Is that some Javascript
>>> widget? I'd blame buggy Javascript before Twitter.
>>
>> I go to twitter.com, log in and press that odd blue compose button in
>> the top-right. After pasting at says I have 135 (down from 140)
>> characters left.
>
> I'm pretty sure that will be a piece of Javascript running in your
> browser that reports the number of characters in the text box. So, I
> would expect that either:
>
> - Javascript doesn't provide a way to normalize text;
>
> - Twitter's Javascript developer(s) don't know how to normalize text, or
> can't be bothered to follow company policy (shame on them);
>
> - the Javascript just asks the browser, and the browser doesn't know how
> to count characters the Twitter way;
>
> etc. But of course posting to Twitter via your browser isn't the only way
> to post. Twitter provide an API to twit, and *that* is the ultimate test
> of whether Twitter's dev guide is lying or not.

Well, I've done some further testing and it seems you're right. It's
just the javascript that's wrong. I guess they did it for better
load-times.

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#52385

Le dimanche 11 août 2013 11:09:44 UTC+2, Steven D'Aprano a écrit :
> On Sun, 11 Aug 2013 07:17:42 +0100, Joshua Landau wrote:
> 
> 
> 
> 
> The reason some accented letters have single code point forms is to 
> 
> support legacy charsets; ...

No.

jmf

PS Unicode normalization is failing expectedly very well
with the FSR.

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#52386

On 11 August 2013 13:51,  <wxjmfauth@gmail.com> wrote:
> Le dimanche 11 août 2013 11:09:44 UTC+2, Steven D'Aprano a écrit :
>> On Sun, 11 Aug 2013 07:17:42 +0100, Joshua Landau wrote:
>>
>> The reason some accented letters have single code point forms is to
>> support legacy charsets; ...
>
> No.
>
> jmf
>
> PS Unicode normalization is failing expectedly very well
> with the FSR.

No.

Joshua Landau

PS Proper arguments are falling expectedly very well with the internet

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