Hang when value-to-print is very large #703

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1. sebastinas

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   frontend-limitations

   on Aug 24, 2017
2. sebastinas commented on Nov 18, 2017

   

   sebastinas

   on Nov 18, 2017

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   From #717: Regression introduced in ef91741.

   👍React with 👍1Reacted by Attila Szöllősi
3. sebastinas commented on Nov 18, 2017

   

   sebastinas

   on Nov 18, 2017

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   Pinging @ata2001.
4. ata2001 commented on Jan 3, 2018

   

   ata2001

   on Jan 3, 2018

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   I'm on it.
5. ata2001 commented on Jan 3, 2018

   

   ata2001

   on Jan 3, 2018

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   Okay, curtsies.formatstring.width_aware_slice() is slow for some reason on long strings. It becomes much faster when you pass the string in smaller chunks.

   For example:

   print("\x1b[31mhello" * 1000)
   

   won't hang because it gets converted to an FmtStr as 1000 chunks instead of one string

   >>> msg = fmtstr("\x1b[31mhello" * 1000)                                                                                                             [42/1785]
   >>> msg
   red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+re
   d('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red(
   'hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('h
   ello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hel
   lo')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello
   ')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')
   +red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+r
   ed('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red
   ('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')+red('hello')...
   
6. ata2001 commented on Jan 4, 2018

   

   ata2001

   on Jan 4, 2018

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   This is definitely a curtsies issue, I'm going to create a PR optimizing curtsies.formatstring.width_aware_slice().
7. BenWiederhake

   added a commit that references this issue on Jan 6, 2018

   Fix quadratic runtime of width_aware_slice

   ...

   a3a94bc
8. BenWiederhake commented on Jan 6, 2018

   

   BenWiederhake

   on Jan 6, 2018

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   I took the freedom of overtaking you.
9. mock commented on Jan 18, 2018

   

   mock

   on Jan 18, 2018

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   is that fix above the solution to the problem or just a workaround?
10. BenWiederhake commented on Jan 19, 2018

    

    BenWiederhake

    on Jan 19, 2018

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    It's the actual solution. At least it takes the part of the code which is responsible for being slow and makes it so fast that it should no longer be the bottleneck.
11. thomasballinger commented on Feb 12, 2018

    

    thomasballinger

    on Feb 12, 2018

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    This has been merged and a new release of Curtsies (0.2.12) has @BenWiederhake's patch. This is a big improvement that will help users now (there are at least 4 issues that are dups of this) so big thanks to @BenWiederhake. The behavior is from the bpython side is still empirically quadratic
    
    so still needs some work.

    Since this was introduced by width_aware_slice in ef91741 we might need to revert that. I don't remember the specific cases this was important for, should figure this out.
12. thomasballinger commented on Feb 14, 2018

    

    thomasballinger

    on Feb 14, 2018

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    I've written a linear version of the line splitting behavior that made this still quadratic despite @BenWiederhake fix in curtsies with bpython/curtsies#110 but in the meantime we've stopped using the width-aware solution and released 0.17.1 to fix this behavior.

    I'm not totally clear on what width-awareness was solving for us – seems like some edge cases around where to wrap lines that have double-width characters or combining characters in them, but there haven't been any open issues about that. Eventually we can use this for formatting input and correctly position the cursor in the case of double-width and combining characters, but no issues open about that. I'm going to hold off on #731 until the case for why we need it is clearer and we're confident it doesn't cause any regressions.
13. thomasballinger

    closed this as completedon Feb 14, 2018