Char type as a special length one string type #4334

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1. elazarg commented on Dec 7, 2017

   

   elazarg

   on Dec 7, 2017

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   I think this is similar (in challenges and special-casing) to having a singleton type. (Imagine unary alphabet; for most purposes mypy doesn't know it's not). But it's less general and requires understanding of len for flow-dependent checking. If we can do this, we might as well add singleton types, and a special "AnyChar" value. Then Char is Singleton[AnyChar].
2. JukkaL commented on Dec 7, 2017

   

   JukkaL

   on Dec 7, 2017

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   I've sometimes wondered about having a character type, but haven't yet found very convincing use cases.

   One option would be to implement this as a separate string-like type with a promotion from Char to Text (similar to the promotion from int to float that we already have). Both would be represented at runtime by the same type. A single-character string literal would have type Char (maybe only in a Char type context, though).

   However, there are probably simpler ways to catch accidentally using str when Iterable[str] or Sequence[str] is expected. For example, we could have a strictness option that would flag these. If we had such option, I'd probably turn it on in codebases that I work on, for sure.
3. JukkaL

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   on Dec 7, 2017
4. JukkaL commented on Jan 29, 2020

   

   JukkaL

   on Jan 29, 2020

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   Literal['x'] can sometimes be used for this use case. More generally, there is no concrete proposal that seems practical, so I'm closing the issue.
5. JukkaL

   closed this as completedon Jan 29, 2020
6. Hibou57 commented on Sep 3, 2020

   

   Hibou57

   on Sep 3, 2020

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   There is also a common misconception about what a character is. There are code points and graphemes. What one sees in a text editor, are graphemes, what a computer sees in a file, are code points. Some graphemes are made of two code points, a code point for a base glyph and a code point for an overlayed glyph.

   As far I experienced it, Python deals with code point, so a grapheme made of two glyphs, will be a string of length 2.

   The best to deal with code points individually, is to deal with their integer value which can be retrieve with the ord() function.

   I would rather say the issue is that Python does not provide a built-in iterator to iterate over a string as a sequence of code point integer values, but one can define such an iterator easily. I also believe there is no Python function to split a string into graphemes, by the way (unless i’m wrong).