Run selection/line in python terminal seems to fail if selected too many characters

[alexanderpils]

Type: Bug

Behaviour

On my MacBook when I select more than around 1100 characters the parsing of the selection is failing and causing then an syntax error when executed in the terminal.

Steps to reproduce:

1. Select more than 1100 characters with some indentations like functions, classes, loops,...

2. Then press shift + enter (Python: Run selection/Line in Python Terminal)

3. Now the data gets parsed wrong and is causing an Error.

screenrecording.mov

Diagnostic data

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

XXX

Extension version: 2026.0.0
VS Code version: Code 1.108.1 (Universal) (585eba7c0c34fd6b30faac7c62a42050bfbc0086, 2026-01-14T14:55:44.241Z)
OS version: Darwin arm64 25.2.0
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.12.12
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): Venv
• Value of the python.languageServer setting: Pylance

User Settings

languageServer: "Pylance"

Installed Extensions

Extension Name	Extension Id	Version
autodocstring	njp	0.6.1
copilot-chat	Git	0.36.1
debugpy	ms-	2025.18.0
echoapi-for-vscode	Ech	1.7.13
gitlens	eam	17.9.0
isort	ms-	2025.0.0
js-debug	ms-	1.105.0
js-debug-companion	ms-	1.1.3
jupyter	ms-	2025.9.1
jupyter-keymap	ms-	1.1.2
jupyter-renderers	ms-	1.3.0
LiveServer	rit	5.7.9
material-icon-theme	PKi	5.30.0
python	ms-	2026.0.0
rainbow-csv	mec	3.24.1
ruff	cha	2026.34.0
vscode-js-profile-table	ms-	1.0.10
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
vscode-pylance	ms-	2025.10.4
vscode-python-envs	ms-	1.16.0
vsliveshare	ms-	1.0.5959
vsliveshare-pack	ms-	0.4.0

System Info

Item	Value
CPUs	Apple M1 Pro (8 x 2400)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: enabled_on trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	2, 3, 4
Memory (System)	16.00GB (0.36GB free)
Process Argv	--crash-reporter-id 6c7f7e46-e60f-4b2b-9859-c46c2fc707c1
Screen Reader	no
VM	0%

A/B Experiments

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pythonvspyt551cf:31249601
binariesv615:30325510
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dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31436602
aj953862:31281341
63221493:31336333
cloudbuttont:31379625
42190218_ostrepl:31403339
use-responses-api:31390855
ec5jj548:31422691
cmp-ext-treat:31426748
cp_cls_c_966_ss:31446431
c0683394:31419495
nes-autoexp-off:31446584
a5gib710:31434435
rename_enabled:31436409
7a04d226_do_not_restore_last_panel_session:31438103
anthropic_thinking_t:31432745
cp_cls_c_1081:31443829
copilot-nes-oct-trt:31432596
nes-jump-on-with-edit:31447383
nes-slash-models-on:31441832
nes-set-to-on:31441941
a43f0576c:31442824
ts_provider_disabled:31446105
nes-conv-1-2:31447851

[anthonykim1]

@alexanderpils Are you getting the message pty connection lost when you send much line into the terminal?

[alexanderpils]

No I don't get a message concerning pty connection lost. I can still send lines to the terminal and execute code.

[spluta]

This happens for me as well on 1.108 and 1.109, but not on 1.107, so I am stuck there. No pty connection lost. Just with lots of lines (40+).

[anthonykim1]

@spluta Could you show a gif?

@alexanderpils @spluta Could you guys set log level to trace and paste the output from terminal and pty host output?

[spluta]

sure. files attached. It didn't like everything pasted in (so there is a file attached). again, this happens in 1.108 and 1.109, but was fine in 1.107

109error.rtf