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BenWiederhake opened this issue Apr 11, 2016 · 8 comments
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Formatting fails when value-to-print is very large #607

BenWiederhake opened this issue Apr 11, 2016 · 8 comments

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@BenWiederhake
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Reproduce with:

  • Start bpython (happens in both bpython version 0.15 on top of Python 3.5.1+ /usr/bin/python3 and bpython version 0.15 on top of Python 2.7.11+ /usr/bin/python)
  • Do something that has at least two screenfuls of output when printed. Example: ["Hello"] * 1000

Expected result: boring stuff. Just the printed "value" of a list that contains a thousand "hello"s.

Actual result: The value, and then some formatting related characters that got garbled:

>>> ["Hello"] * 1000
['Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
[... SNIP ...]
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello',
 'Hello', 'Hello', 'Hello', 'Hello', 'Hello', 'Hello']�[-26;1H
>>>

Note the trailing U+001B which smells like formatting gone wrong.

I'm not sure whether this is a bug in xfce4-terminal 0.6.3, bpython, bpython-curtsies, curtsies, or maybe something else entirely. However, bpython is the only program exhibiting this behavior, so I reported it here.
@thomasballinger
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I bet this is some nonstandard terminal formatting that curtsies is doing. I can't reproduce at the moment, but will try soon with xfce.

@thomasballinger
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/me still hasn't tried with xfce

I'm guessing something's happening to the math in Curtsies such that the "Cursor Home" command that moves the cursor <ESC>[{ROW};{COLUMN}H came out with a negative row here. I checked and Blessings passes through negative numbers to its Terminal.move command, so this is possible.

So probably one of the numbers in cursor_pos[0] - offscreen_scrolls + self.top_usable_row is bad, but I don't know which. I don't have a Linux machine around at the moment to check.

@thomasballinger
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thomasballinger commented Jun 7, 2016 •
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It turns out this is happening in my terminal too, but iTerm2 swallows the invalid sequence! It's likely a Curtsies issue, these sequence may not be doing anything important, I'll look into it more.

@thomasballinger
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I noticed in a gif I uploaded for another reason that the cursor disappears sometimes, and I think this may be related based on the Curtsies source: the sequence to make the cursor visible is written just after this sequence that is sometimes negative.
asciicast

@thomasballinger
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I suspect this is the problem but haven't nicely reproduced it. @BenWiederhake if it's not much trouble would you try pip install git+https://github.com/thomasballinger/curtsies.git@fix-bpython-607 to see if it fixes the problem?

@BenWiederhake
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Appears to work, thanks :D

(For fun I pip uninstalled this version of curtsies again, as a sanity check of sorts, and indeed: with the old system version, it still shows the faulty behavior, so your fix definitely works.)

@thomasballinger
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Great, I've merged that and will do a Curtsies release before long, so at least fresh installations of Curtsies will have it fixed. I'll leave this open until I've done that Curtsies release.

@sebastinas
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A new version of curtsies has been released in the meantime.

@BenWiederhake BenWiederhake mentioned this issue Aug 23, 2017
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@sebastinas @thomasballinger @BenWiederhake