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You can't truncate a sequence of Unicode codepoints without the risk of producing a broken string, either. What do you get if you truncate "Åström" after the

You can't truncate a sequence of Unicode codepoints without the risk of producing a broken string, either. What do you get if you truncate "Åström" after the first "o"? What do you get if you truncate 🇨🇦 after the first codepoint? Normalization is not a real solution unless you restrict yourself to working with well-edited formal prose in common Western languages. This is not a claim made from ignorance.

lolc 6y ago
Sorry, we're mixing two layers. Of course, if I truncate a string, it may lose its meaning. And having accents fall off is problematic. But it's not the same as truncating a byte-array, because then an invalid sequence of bytes may result. Stop treating these cases as equivalent. They're not.
- naniwaduni 6y ago
  They are equivalent. The only reason you find it problematic that a sequence of bytes is "invalid" (read: can't be decoded in your preferred encoding) is because you've manufactured the problem. In the end, the only layer at which it really matters whether your byte sequence can be decoded is the font renderer, and just being valid utf-8 isn't good enough for it either.
  - lolc 6y ago
    > In the end, the only layer at which it really matters whether your byte sequence can be decoded is the font renderer Ok that explains how we ended up here. I'm considering some other common uses! A search-index for example greatly profits from being able to normalize representations and split words.
    - naniwaduni 6y ago
      Search index use cases probably also benefit from normalizing inputs across encodings, that's no shining example of utf-8-onlyism. You can still best-effort split words! You can do a pretty good job splitting words without ensuring that the words decode in your preferred encoding.
      - lolc 6y ago
        Here's the thing: I don't want to work in UTF8. I want to work in Unicode. Big difference. Because tracking the encoding of my strings would increase complexity. So at the earliest convenience, I validate my assumptions about encoding and let a lower layer handle it from then on. I understand you're arguing about some sort of equivalency between byte-arrays and Unicode strings. Sure there are half-baked ways to do word-splitting on a byte-array. But why do you consider that a viable option? Under what circumstances would you do that?
        naniwaduni 6y ago
        Every circumstance. Why do you consider it unviable? What problems do you think having a Unicode sequence solves?
        lolc 6y ago
        Convince me. Here's a little library function that turns text into a set of words: def keywords(text): return set(filter(None, re.split("\W+", unicodedata.normalize("NFKC", input_str).lower()))) How would this look if strings were byte-arrays? How would `normalize()`, `lower()`, and `split()` know what encoding to use? The way I see it: If the encoding is implicit, you have global state. If it's explicit, you have to pass the encoding. Both is extra state to worry about. When the passed value is a Unicode string, this question doesn't come up.
        naniwaduni 6y ago
        It looks pretty much the some, except that you assume the input is already in your library's canonical encoding (probably utf-8 nowadays). I realize this sounds like a total cop-out, but when the use-case is destructively best-effort tokenizing an input string using library functions, it doesn't really matter whether your internal encoding is utf-32 or utf-8. I mean, under the hood, normalize still has to map arbitrary-length sequences to arbitrary-length sequences even when working with utf-32 (see: unicodedata.normalize("NFKC", "a\u0301 ﬃ") == "\xe1 ffi"). So on the happy path, you don't see much of a difference. The main observable difference is that if you take input without decoding it explicitly, then the always-decode approach has already crashed long before reaching this function, while the assume-the-encoding approach probably spouts gibberish at this point. And sure, there are plenty of plausible scenarios where you'd rather get the crash than subtly broken behaviour. But ... I don't see this reasonably being one of them, considering that you're apparently okay with discarding all \W+.
- Jasper_ 6y ago
  So in one case, the text becomes corrupted and unreadable (i.e. loses its meaning), and in the other, it becomes corrupted and unreadable. What's the difference? Having "accents fall off" has gotten people murdered [0]. Accents aren't things peppered in for effect, they turn letters into different letters, spelling different words. Analogously, imagine that a bunch of software accidentally turned every "d" into a "c" because some committee halfway around the world decided "d" should be composed of the "c" and "|" glyphs. That's the kind of text corruption that regularly happens in other languages when dealing with text at the code point layer. [0] https://languagelog.ldc.upenn.edu/nll/?p=73 https://languagelog.ldc.upenn.edu/nll/?p=73 . Note that this is Turkish, which has the "dotted i" problem, meaning that this was more than likely a .toupper() gone wrong rather than a truncation issue.
  - lolc 6y ago
    The difference is that for truncating, I can work within Unicode to deal with the situation. I can accept the possibility of mutilated letters, I can convert to NFC, I can truncate on word-boundaries, I have choice. If I have an byte-array, I can do none of these things short of implementing a good chunk of Unicode. If I truncate, I risk ending up with an invalid UTF-8 string. End of story.
    - tsimionescu 6y ago
      And what is wrong with an invalid UTF-8 string? Why were you truncating the string in the first place? Basically, I believe the point here is that a Unicode aware truncation should be done in a Unicode aware truncate method. There is no good reason to parse a string as UTF-8 ahead of time - just keep it as a blob of bytes until you need to do some something "texty" with it. It is the truncate-at-word-boundaries() method that should interpret the bytes as UTF-8 and fail if they are not valid. Why parse it sooner?
    - Jasper_ 6y ago
      > If I have an byte-array, I can do none of these things short of implementing a good chunk of Unicode. If I truncate, I risk ending up with an invalid UTF-8 string. Yes, and? You can have an invalid sequence of Unicode code points too, such as an unpaired surrogate (something Python's text model actually abuses to store "invalid Unicode" in a special, non-standard way). If you truncate at the byte level, you are just truncating "between code points"; it's a closer granularity than at the code point layer, so you can also convert to NFC, truncate on word boundaries, etc. You just need to ignore the parts of the UTF-8 string that are invalid; which isn't difficult, because UTF-8 is self-synchronizing.

lolc 6y ago

Sorry, we're mixing two layers. Of course, if I truncate a string, it may lose its meaning. And having accents fall off is problematic. But it's not the same as truncating a byte-array, because then an invalid sequence of bytes may result. Stop treating these cases as equivalent. They're not.

naniwaduni 6y ago
They are equivalent. The only reason you find it problematic that a sequence of bytes is "invalid" (read: can't be decoded in your preferred encoding) is because you've manufactured the problem. In the end, the only layer at which it really matters whether your byte sequence can be decoded is the font renderer, and just being valid utf-8 isn't good enough for it either.
- lolc 6y ago
  > In the end, the only layer at which it really matters whether your byte sequence can be decoded is the font renderer Ok that explains how we ended up here. I'm considering some other common uses! A search-index for example greatly profits from being able to normalize representations and split words.
  - naniwaduni 6y ago
    Search index use cases probably also benefit from normalizing inputs across encodings, that's no shining example of utf-8-onlyism. You can still best-effort split words! You can do a pretty good job splitting words without ensuring that the words decode in your preferred encoding.
    - lolc 6y ago
      Here's the thing: I don't want to work in UTF8. I want to work in Unicode. Big difference. Because tracking the encoding of my strings would increase complexity. So at the earliest convenience, I validate my assumptions about encoding and let a lower layer handle it from then on. I understand you're arguing about some sort of equivalency between byte-arrays and Unicode strings. Sure there are half-baked ways to do word-splitting on a byte-array. But why do you consider that a viable option? Under what circumstances would you do that?
      - naniwaduni 6y ago
        Every circumstance. Why do you consider it unviable? What problems do you think having a Unicode sequence solves?
        lolc 6y ago
        Convince me. Here's a little library function that turns text into a set of words: def keywords(text): return set(filter(None, re.split("\W+", unicodedata.normalize("NFKC", input_str).lower()))) How would this look if strings were byte-arrays? How would `normalize()`, `lower()`, and `split()` know what encoding to use? The way I see it: If the encoding is implicit, you have global state. If it's explicit, you have to pass the encoding. Both is extra state to worry about. When the passed value is a Unicode string, this question doesn't come up.
        naniwaduni 6y ago
        It looks pretty much the some, except that you assume the input is already in your library's canonical encoding (probably utf-8 nowadays). I realize this sounds like a total cop-out, but when the use-case is destructively best-effort tokenizing an input string using library functions, it doesn't really matter whether your internal encoding is utf-32 or utf-8. I mean, under the hood, normalize still has to map arbitrary-length sequences to arbitrary-length sequences even when working with utf-32 (see: unicodedata.normalize("NFKC", "a\u0301 ﬃ") == "\xe1 ffi"). So on the happy path, you don't see much of a difference. The main observable difference is that if you take input without decoding it explicitly, then the always-decode approach has already crashed long before reaching this function, while the assume-the-encoding approach probably spouts gibberish at this point. And sure, there are plenty of plausible scenarios where you'd rather get the crash than subtly broken behaviour. But ... I don't see this reasonably being one of them, considering that you're apparently okay with discarding all \W+.
Jasper_ 6y ago
So in one case, the text becomes corrupted and unreadable (i.e. loses its meaning), and in the other, it becomes corrupted and unreadable. What's the difference? Having "accents fall off" has gotten people murdered [0]. Accents aren't things peppered in for effect, they turn letters into different letters, spelling different words. Analogously, imagine that a bunch of software accidentally turned every "d" into a "c" because some committee halfway around the world decided "d" should be composed of the "c" and "|" glyphs. That's the kind of text corruption that regularly happens in other languages when dealing with text at the code point layer. [0] https://languagelog.ldc.upenn.edu/nll/?p=73 https://languagelog.ldc.upenn.edu/nll/?p=73 . Note that this is Turkish, which has the "dotted i" problem, meaning that this was more than likely a .toupper() gone wrong rather than a truncation issue.
- lolc 6y ago
  The difference is that for truncating, I can work within Unicode to deal with the situation. I can accept the possibility of mutilated letters, I can convert to NFC, I can truncate on word-boundaries, I have choice. If I have an byte-array, I can do none of these things short of implementing a good chunk of Unicode. If I truncate, I risk ending up with an invalid UTF-8 string. End of story.
  - tsimionescu 6y ago
    And what is wrong with an invalid UTF-8 string? Why were you truncating the string in the first place? Basically, I believe the point here is that a Unicode aware truncation should be done in a Unicode aware truncate method. There is no good reason to parse a string as UTF-8 ahead of time - just keep it as a blob of bytes until you need to do some something "texty" with it. It is the truncate-at-word-boundaries() method that should interpret the bytes as UTF-8 and fail if they are not valid. Why parse it sooner?
  - Jasper_ 6y ago
    > If I have an byte-array, I can do none of these things short of implementing a good chunk of Unicode. If I truncate, I risk ending up with an invalid UTF-8 string. Yes, and? You can have an invalid sequence of Unicode code points too, such as an unpaired surrogate (something Python's text model actually abuses to store "invalid Unicode" in a special, non-standard way). If you truncate at the byte level, you are just truncating "between code points"; it's a closer granularity than at the code point layer, so you can also convert to NFC, truncate on word boundaries, etc. You just need to ignore the parts of the UTF-8 string that are invalid; which isn't difficult, because UTF-8 is self-synchronizing.