Python syntax highlighting is unbearably slow

Type: Bug

Using the latest vscode-insiders, Python language error checking and syntax highlighting is extremely slow - it seems to be re-processing the file at every single keystroke state, and managing to get through not even three of those processes per second. Any other file or code actions (saving, closing, autocomplete, anything) must also wait for it to catch up with the keystrokes.

This got annoying enough that I actually installed the stable version of vscode. I can confirm that the stable release does not have this bug, with the exact same (synced) settings and extensions and in the same workspace.

VS Code version: Code - Insiders 1.130.0-insider (5e212606d57c0a17f73bc8b7ae0cc9e14bcfd345, 2026-07-17T16:24:39Z)
OS version: Windows_NT x64 10.0.19045
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|11th Gen Intel(R) Core(TM) i5-11600KF @ 3.90GHz (12 x 3912)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x10de, DEVICE=0x1b82 [NVIDIA GeForce GTX 1070 Ti], DRIVER_VENDOR=NVIDIA, DRIVER_VERSION=32.0.15.6094 *ACTIVE*
GPU1: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.19041.5794
Machine model name:
Machine model version:
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: disabled_off
trees_in_viz: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgpu: enabled
webnn: disabled_off|
|Load (avg)|undefined|
|Memory (System)|15.89GB (4.06GB free)|
|Process Argv|--folder-uri file:///c%3A/Users/Nixill/Documents/Git/Python-Nixill.Color --crash-reporter-id eaa957b1-6421-4350-86e9-44de8f4ee528|
|Screen Reader|no|
|VM|0%|
Extensions (62)

Name|Identifier|Author|Version
---|---|---|---
SQLite|alexcvzz.vscode-sqlite|alexcvzz|0.14.1
NuGet Package Manager GUI|aliasadidev.nugetpackagemanagergui|aliasadidev|2.1.1
G-Code Syntax|appliedengdesign.vscode-gcode-syntax|appliedengdesign|0.7.7
Avalonia for VSCode|avaloniateam.vscode-avalonia|AvaloniaTeam|12.3.0
Auto Splitting Language|b0sh.asl-extension|B0sh|1.1.0
gitignore|codezombiech.gitignore|codezombiech|0.10.0
Delete File and Keep Open|davidalejandroaguilar.delete-file-and-keep-open|davidalejandroaguilar|1.0.2
GitLens — Git supercharged|eamodio.gitlens|eamodio|2026.7.180533
EditorConfig|editorconfig.editorconfig|EditorConfig|0.18.2
Debugger for Firefox|firefox-devtools.vscode-firefox-debug|firefox-devtools|2.15.0
SCS Script|frankity.scs-script|Frankity|0.0.6
GitHub Codespaces|github.codespaces|GitHub|1.18.15
GitHub Actions|github.vscode-github-actions|github|0.32.3
CraftOS-PC for VS Code|jackmacwindows.craftos-pc|JackMacWindows|1.2.3
ComputerCraft|jackmacwindows.vscode-computercraft|JackMacWindows|1.1.1
NuGet Package Manager|jmrog.vscode-nuget-package-manager|jmrog|1.1.6
AHK++ (AutoHotkey Plus Plus)|mark-wiemer.vscode-autohotkey-plus-plus|mark-wiemer|6.7.3
Rainbow CSV|mechatroner.rainbow-csv|mechatroner|3.24.1
syntax-mcfunction|minecraftcommands.syntax-mcfunction|MinecraftCommands|1.0.1
JSON5 syntax|mrmlnc.vscode-json5|mrmlnc|1.0.0
C# Dev Kit|ms-dotnettools.csdevkit|ms-dotnettools|3.20.199
C#|ms-dotnettools.csharp|ms-dotnettools|2.146.2
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0
Python Debugger|ms-python.debugpy|ms-python|2026.7.11831010
isort|ms-python.isort|ms-python|2026.7.11891015
Python|ms-python.python|ms-python|2026.5.2026070801
Pylance|ms-python.vscode-pylance|ms-python|2026.2.109
Python Environments|ms-python.vscode-python-envs|ms-python|1.37.2026070201
Jupyter|ms-toolsai.jupyter|ms-toolsai|2026.6.2026071501
Jupyter Keymap|ms-toolsai.jupyter-keymap|ms-toolsai|1.1.2
Jupyter Notebook Renderers|ms-toolsai.jupyter-renderers|ms-toolsai|1.3.0
Jupyter Cell Tags|ms-toolsai.vscode-jupyter-cell-tags|ms-toolsai|0.1.9
Jupyter Slide Show|ms-toolsai.vscode-jupyter-slideshow|ms-toolsai|0.1.6
Remote - SSH|ms-vscode-remote.remote-ssh|ms-vscode-remote|0.124.0
Remote - SSH: Editing Configuration Files|ms-vscode-remote.remote-ssh-edit|ms-vscode-remote|0.87.0
WSL|ms-vscode-remote.remote-wsl|ms-vscode-remote|0.104.3
Hex Editor|ms-vscode.hexeditor|ms-vscode|1.11.1
Remote Explorer|ms-vscode.remote-explorer|ms-vscode|0.5.0
Word Count|ms-vscode.wordcount|ms-vscode|0.1.0
Live Share|ms-vsliveshare.vsliveshare|ms-vsliveshare|1.1.122
Fix JSON|oliversturm.fix-json|oliversturm|0.2.0
Geo Data Viewer|randomfractalsinc.geo-data-viewer|RandomFractalsInc|2.6.0
Language Support for Java(TM) by Red Hat|redhat.java|redhat|1.55.0
XML|redhat.vscode-xml|redhat|0.29.2026061109
csproj Extensions|selcukermaya.se-csproj-extensions|selcukermaya|0.0.7
Markdown Preview Enhanced|shd101wyy.markdown-preview-enhanced|shd101wyy|0.8.30
Liquid|sissel.shopify-liquid|sissel|4.0.1
Zip File Explorer|slevesque.vscode-zipexplorer|slevesque|0.3.1
Datapack Helper Plus by Spyglass|spgoding.datapack-language-server|SPGoding|4.9.1
Lua|sumneko.lua|sumneko|3.18.2
Even Better TOML|tamasfe.even-better-toml|tamasfe|0.21.2
open in browser|techer.open-in-browser|techer|2.0.0
AutoHotkey v2 Language Support|thqby.vscode-autohotkey2-lsp|thqby|3.0.10
Rainbow Tags|voldemortensen.rainbow-tags|voldemortensen|0.4.1
Gradle for Java|vscjava.vscode-gradle|vscjava|3.18.0
Debugger for Java|vscjava.vscode-java-debug|vscjava|0.59.0
Project Manager for Java|vscjava.vscode-java-dependency|vscjava|0.27.6
Extension Pack for Java|vscjava.vscode-java-pack|vscjava|0.31.1
Test Runner for Java|vscjava.vscode-java-test|vscjava|0.46.0
Maven for Java|vscjava.vscode-maven|vscjava|0.45.3
Markdown All in One|yzhang.markdown-all-in-one|yzhang|3.6.3
vscode-autohotkey-debug|zero-plusplus.vscode-autohotkey-debug|zero-plusplus|1.11.1

A/B Experiments

```
vsliv368cf:30146710
pythonvspyt551cf:31249598
nativeloc1:31118317
dwcopilot:31158714
dwoutputs:31242946
copilot_t_ci:31333650
g012b348:31231168
pythonrdcb7:31268811
pythonpcpt1:31399616
6518g693:31302842
63221493:31336333
envsactivate1:31349248
editstats-enabled:31346256
cloudbuttont:31366566
3efgi100_wstrepl:31403338
cp_cls_t_966_ss:31526232
4je02754:31455664
c3h7c220:31478652
38bie571_auto:31426784
cp_cls_t_1081:31454832
conptydll_true:31485575
e9c30283:31453065
test_treatment2:31471001
46204921:31447328
idci7584:31454084
e3e4d672:31454087
ei9d7968:31462942
f860i809:31458078
7e884298:31462391
7e187181:31482583
githubstableflight:31469463
h08i8180_copy:31475366
ec1eg703:31520046
ddid_t:31478204
hmra_i5g22:31518061
bjc72774_agent_sandbox:31538428
7df3h592:31491241
cp_cls_t_1082:31535311
logging_enabled_new:31490725
jb_cp_cls_t_632:31543129
32d76977:31503652
ha629193:31508444
cdk-lw-on:31524445
f9bf7985:31541111
a1ije391_t:31533808
41836166:31537719
jbcp_cls_pctr_t:31531130
cp_intellij_t_nes:31548657
jf4hg949:31526829
hide-eh-duplicates:31543293
h561g132:31534507
replace-eh-with-ah:31545853
ihg5j128:31534457
f412h606:31543414
enable_editor_pane_layout:31551200
52258b4d:31547953
c7c27ce7:31551212

```