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 -- http://mail.python.org/mailman/listinfo/python-list
