Description

treyhunner

opened on Jun 3, 2025

Issue body actions

Bug report

Bug description:

In Python 3.14 beta 2, pasting code that has more lines than the height of my terminal window will result in the lines just above the terminal window being blank.

To reproduce:

1. Resize your terminal so the height is approximately 20 rows
2. Paste the below block of Python code.
3. Scroll up in your terminal to see previous lines above the last 20 rows
4. Note that all rows above the terminal screen are blank (no class Point: line or __slots__ line for example)

class Point:
    __slots__ = ('x', 'y')
    __match_args__ = ('x', 'y')

    def __init__(self, x: float, y: float) -> None:
        object.__setattr__(self, 'x', x)
        object.__setattr__(self, 'y', y)

    def __repr__(self):
        cls = type(self).__name__
        return f'{cls}(x={self.x!r}, y={self.y!r})'

    def __eq__(self, other):
        if not isinstance(other, Point):
            return NotImplemented
        return (self.x, self.y) == (other.x, other.y)

    def __hash__(self):
        return hash((self.x, self.y))

    def __setattr__(self, name, value):
        raise AttributeError(f"Can't set attribute {name!r}")

    def __delattr__(self, name):
        raise AttributeError(f"Can't delete attribute {name!r}")

    def __getstate__(self):
        return (self.x, self.y)

    def __setstate__(self, state):
        fields = ('x', 'y')
        for field, value in zip(fields, state):
            object.__setattr__(self, field, value)

This is essentially the same as the "Blank lines" section of issue #119517.

I assume this is being done for performance reasons, but this is going to make my life harder when teaching. I often use a large font when teaching, so it's not uncommon that I'll paste a block of code that is longer than the terminal height. Being able to scroll up and show my students what was pasted is an essential feature for me when teaching.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Activity

1. treyhunner

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Jun 3, 2025
2. emmatyping

   added

   topic-replRelated to the interactive shellRelated to the interactive shell

   3.14bugs and security fixesbugs and security fixes

   3.15bugs and security fixesbugs and security fixes

   on Jun 3, 2025
3. tomasr8 commented on Jun 3, 2025

   

   tomasr8

   on Jun 3, 2025

   Member

   More actions

   Bisected to fac41f5 (#133247)

   Reacted by Trey Hunner
4. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Jun 7, 2025
5. treyhunner commented on Jul 8, 2025

   

   treyhunner

   on Jul 8, 2025

   MemberAuthor

   More actions

   I just confirmed that this is still an issue in 3.14.0b4.

   Another way to reproduce:

   • Resize your terminal window to have few rows
   • Paste a large multi-line string
   • Resize your terminal window to be normally sized on your machine
   • Witness the blank lines above the last few rows of pasted text

   
6. treyhunner commented on Sep 2, 2025

   

   treyhunner

   on Sep 2, 2025

   MemberAuthor

   More actions

   This is still an issue with the 3.14rc2 and this may keep me from using 3.14 while teaching. The syntax highlighting is really great, but this regression is a pretty big issue when live-coding in the REPL.

   @ambv, assuming this change in behavior was to improve performance while pasting, would not highlighting large blocks of text (or not highlighting text shown before the current terminal view) improve performance enough to allow showing the whole text block?
7. ambv commented on Sep 15, 2025

   

   ambv

   on Sep 15, 2025

   Contributor

   More actions

   IPython does what we're doing now as well. Code that is outside of the visible viewport is not emitted. We are still emitting empty lines, which is in itself a bug (it's not useful and IPython doesn't do it). I'll fix that.

   The change was indeed made to make pasting faster, so I'll look into whether bulk-emitting non-highlighted code past the scrollback barrier is feasible.

   Reacted by Trey Hunner
8. chris-eibl commented on Sep 16, 2025

   

   chris-eibl

   on Sep 16, 2025

   Member

   More actions

   Maybe emitting highlighted code past the scrollback can be done in a different paste mode like

   F4: enter "full" paste mode (press again to exit)

   and / or using CTRL-SHIFT-v (or whatever short cut seems more appropriate)?
9. StanFromIreland

   marked Pasting large blocks of code into the console causes the code to be truncated #137979 as a duplicate of this issue on May 30, 2026

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