KeyError after VSCode update

[Flamefire]

Diagnostic Data

• Python version (& distribution if applicable, e.g., Anaconda): 3.11.3
• Type of virtual environment used (e.g., conda, venv, virtualenv, etc.): venv
• Operating system (and version): Linux Mint 22.3
• Version of tool extension you are using: 2026.4.0

Behaviour

Actual Behavior

Linting fails with KeyError in logs

Reproduction Steps:

Open Python file and/or modify & save it.

Logs:

Click here for detailed logs

2026-04-29 11:06:38.604 [info] CWD Linter: /home/alex/easybuild-easyblocks 2026-04-29 11:06:38.624 [info] [Trace - 11:06:38] Received notification 'window/logMessage'. 2026-04-29 11:06:38.625 [info] Params: { "type": 1, "message": "Traceback (most recent call last):\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py\", line 34, in make\n format_plugin = reporters[format_name]\n ~~~~~~~~~^^^^^^^^^^^^^\nKeyError: \"'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'\"\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py\", line 921, in _run_tool_on_document\n result = utils.run_module(\n ^^^^^^^^^^^^^^^^^\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py\", line 259, in run_module\n return _run_module(module, argv, use_stdin, source)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py\", line 246, in _run_module\n runpy.run_module(module, run_name=\"__main__\")\n File \"\", line 229, in run_module\n File \"\", line 88, in _run_code\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/__main__.py\", line 7, in \n raise SystemExit(main())\n ^^^^^^\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py\", line 23, in main\n app.run(argv)\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py\", line 198, in run\n self._run(argv)\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py\", line 186, in _run\n self.initialize(argv)\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py\", line 172, in initialize\n self.make_formatter()\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py\", line 72, in make_formatter\n self.formatter = reporter.make(self.plugins.reporters, self.options)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py\", line 40, in make\n format_plugin = reporters[\"default\"]\n ~~~~~~~~~^^^^^^^^^^^\nKeyError: 'default'\n" }

2026-04-29 11:06:38.625 [info] [Error - 11:06:38] Traceback (most recent call last):
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 34, in make
format_plugin = reporters[format_name]
~~~~~~~~~^^^^^^^^^^^^^
KeyError: "'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 921, in _run_tool_on_document
result = utils.run_module(
^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 259, in run_module
return _run_module(module, argv, use_stdin, source)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 246, in _run_module
runpy.run_module(module, run_name="main")
File "", line 229, in run_module
File "", line 88, in _run_code
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main.py", line 7, in
raise SystemExit(main())
^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py", line 23, in main
app.run(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 198, in run
self._run(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 186, in _run
self.initialize(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 172, in initialize
self.make_formatter()
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 72, in make_formatter
self.formatter = reporter.make(self.plugins.reporters, self.options)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 40, in make
format_plugin = reporters["default"]
~~~~~~~~~^^^^^^^^^^^
KeyError: 'default'

2026-04-29 11:06:38.625 [info] [Trace - 11:06:38] Received notification 'window/showMessage'.
2026-04-29 11:06:38.625 [info] Params: {
"type": 1,
"message": "Traceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 34, in make\n format_plugin = reporters[format_name]\n ~~~~~~~~~^^^^^^^^^^^^^\nKeyError: "'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'"\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 921, in _run_tool_on_document\n result = utils.run_module(\n ^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 259, in run_module\n return _run_module(module, argv, use_stdin, source)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 246, in _run_module\n runpy.run_module(module, run_name="main")\n File "", line 229, in run_module\n File "", line 88, in _run_code\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main.py", line 7, in \n raise SystemExit(main())\n ^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py", line 23, in main\n app.run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 198, in run\n self._run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 186, in _run\n self.initialize(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 172, in initialize\n self.make_formatter()\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 72, in make_formatter\n self.formatter = reporter.make(self.plugins.reporters, self.options)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 40, in make\n format_plugin = reporters["default"]\n ~~~~~~~~~^^^^^^^^^^^\nKeyError: 'default'\n"
}

2026-04-29 11:06:38.625 [info] [Trace - 11:06:38] Received notification 'window/logMessage'.
2026-04-29 11:06:38.625 [info] Params: {
"type": 1,
"message": "Linting failed with error:\r\nTraceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 34, in make\n format_plugin = reporters[format_name]\n ~~~~~~~~~^^^^^^^^^^^^^\nKeyError: "'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'"\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 319, in _linting_helper\n result = _run_tool_on_document(document, use_stdin=False)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 921, in _run_tool_on_document\n result = utils.run_module(\n ^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 259, in run_module\n return _run_module(module, argv, use_stdin, source)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 246, in _run_module\n runpy.run_module(module, run_name="main")\n File "", line 229, in run_module\n File "", line 88, in _run_code\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main.py", line 7, in \n raise SystemExit(main())\n ^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py", line 23, in main\n app.run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 198, in run\n self._run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 186, in _run\n self.initialize(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 172, in initialize\n self.make_formatter()\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 72, in make_formatter\n self.formatter = reporter.make(self.plugins.reporters, self.options)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 40, in make\n format_plugin = reporters["default"]\n ~~~~~~~~~^^^^^^^^^^^\nKeyError: 'default'\n"
}

2026-04-29 11:06:38.625 [info] [Error - 11:06:38] Linting failed with error:
Traceback (most recent call last):
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 34, in make
format_plugin = reporters[format_name]
~~~~~~~~~^^^^^^^^^^^^^
KeyError: "'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 319, in _linting_helper
result = _run_tool_on_document(document, use_stdin=False)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 921, in _run_tool_on_document
result = utils.run_module(
^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 259, in run_module
return _run_module(module, argv, use_stdin, source)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 246, in _run_module
runpy.run_module(module, run_name="main")
File "", line 229, in run_module
File "", line 88, in _run_code
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main.py", line 7, in
raise SystemExit(main())
^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py", line 23, in main
app.run(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 198, in run
self._run(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 186, in _run
self.initialize(argv)
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 172, in initialize
self.make_formatter()
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 72, in make_formatter
self.formatter = reporter.make(self.plugins.reporters, self.options)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 40, in make
format_plugin = reporters["default"]
~~~~~~~~~^^^^^^^^^^^
KeyError: 'default'

2026-04-29 11:06:38.625 [info] [Trace - 11:06:38] Received notification 'window/showMessage'.
2026-04-29 11:06:38.625 [info] Params: {
"type": 1,
"message": "Linting failed with error:\r\nTraceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 34, in make\n format_plugin = reporters[format_name]\n ~~~~~~~~~^^^^^^^^^^^^^\nKeyError: "'%(row)d,%(col)d,%(code).1s,%(code)s:%(text)s'"\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 319, in _linting_helper\n result = _run_tool_on_document(document, use_stdin=False)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_server.py", line 921, in _run_tool_on_document\n result = utils.run_module(\n ^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 259, in run_module\n return _run_module(module, argv, use_stdin, source)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/tool/lsp_utils.py", line 246, in _run_module\n runpy.run_module(module, run_name="main")\n File "", line 229, in run_module\n File "", line 88, in _run_code\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main.py", line 7, in \n raise SystemExit(main())\n ^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/cli.py", line 23, in main\n app.run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 198, in run\n self._run(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 186, in _run\n self.initialize(argv)\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 172, in initialize\n self.make_formatter()\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/main/application.py", line 72, in make_formatter\n self.formatter = reporter.make(self.plugins.reporters, self.options)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File "/home/alex/.vscode/extensions/ms-python.flake8-2026.4.0/bundled/libs/flake8/plugins/reporter.py", line 40, in make\n format_plugin = reporters["default"]\n ~~~~~~~~~^^^^^^^^^^^\nKeyError: 'default'\n"
}

Outcome When Attempting Debugging Steps:

Running tool command fails as I'm using the bundled flake8 so it's not found when using the console

[michaels19802]

Seeing the same. Rollback to previous version fixes it

[mhearne-usgs]

Seeing the same error. Rolling back to a version from 2 weeks ago did not fix it, rolling back to version from 4 months ago causes errors with the isort client.

[VolodyaCO]

I see a similar error.

[kaiyichangwork-bit]

Same issue here.

[daanbl]

Seeing the same error. Rolling back to a version from 2 weeks ago did not fix it, rolling back to version from 4 months ago causes errors with the isort client.

I rolled back both flake8 and isort to the previous stable releases (2025.2 and 2025.0.0) which seemed to fix the errors. Looks like both packages introduced issues in their latest release.

[JakeSkelton]

I rolled back both flake8 and isort to the previous stable releases (2025.2 and 2025.0.0) which seemed to fix the errors. Looks like both packages introduced issues in their latest release.

This fix worked for me

[Dante-Basile]

Issue does not seem to be VS Code version dependent as far as I can tell.