Python, Python Debugger, and Pylance extensions fail to activate inside Dev Container after rebuilding

[AlexandraDobrescu]

I have reinstalled VSCode on my Mac, by completely removing it and clearing all caches, both the latest version and an older stable version.

After building the dev container, I get errors stating that the Python, Python Debugger, and Pylance extensions cannot activate. Specifically, Pylance fails to connect to its language server.

Here are the extensions I have installed inside the container:

Which are installed inside the container:

This issue makes development very difficult because even though the container builds successfully, I cannot run or debug my Python code inside the container.

I am happy to provide any additional information or logs that might help diagnose this issue. I hope this can be resolved soon, and thank you in advance for your support!

Alexandra

[github-actions]

Hi @AlexandraDobrescu, I'm an AI Support assistant here to help with your issue. While the team reviews your request, I wanted to provide some possible tips and documentation that might help you in the meantime.

---

Potentially Related Issues:

• Dependency mismatches between Pylance and the Python extension causing activation issues – see #6322
• Pylint client failing to connect to the language server, similar to language server connection failures – see #4324
• Inconsistent extension activation and fallback behavior resulting in missing highlights – see #6442

---

The team will respond to your issue shortly. Please note this is a trial feature and may not be fully accurate. I hope these suggestions are helpful in the meantime. If this comment helped you, please give it a 👍. If the suggestion was not helpful or was incorrect, please give it a 👎. Your feedback helps us improve!

[rchiodo]

Transferring to Python extension. If it doesn't initialize, none of the other extensions will work.

@AlexandraDobrescu can you provide the output of the Developer Tools Console? If you go to 'Help | Toggle Developer Tools', that should bring up a separate window. Theoretically there should be an error there related to starting the python extension.

[AlexandraDobrescu]

Hi @rchiodo, thanks for the guidance!

I opened the Developer Tools Console via Help > Toggle Developer Tools as suggested. In the meantime, I also added the "ms-python.vscode-pylance" extension to the devcontainer.json.

Here is the output from the Developer Tools Console:

log.ts:460   ERR Qa: Unable to delete nonexistent file '/Users/alexandradobrescu/Library/Application Support/Code/CachedExtensionVSIXs/ms-python.vscode-pylance-2025.5.1'
    at Apt.X (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3235:69691)
    at async Apt.del (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3235:69913)
    at async Gmt.mb (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3265:14072)
    at async Gmt.lb (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3265:13579)
    at async Gmt.installFromGallery (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3265:12465)
    at async Promise.allSettled (index 1)
    at async ovt.j (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:3297:21198)
error @ log.ts:460
log.ts:460   ERR Cannot read properties of undefined (reading 'identifier'): TypeError: Cannot read properties of undefined (reading 'identifier')
    at get identifier (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2505:12546)
    at jI.setExtensionsControlManifest (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2509:1397)
    at iie.N (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2509:6437)
error @ log.ts:460
log.ts:440  INFO Successfully installed 'ms-python.python' extension
log.ts:460   ERR TreeError [DebugRepl] Tree input not set: Error: TreeError [DebugRepl] Tree input not set
    at Gf.C (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:417:29043)
    at Gf.updateChildren (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:417:28950)
    at Wne.value (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:2092:33670)
    at E.B (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:29:2392)
    at E.C (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:29:2462)
    at E.fire (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:29:2680)
    at x1e.setVisible (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:680:2727)
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:1308:11769
    at Array.map (<anonymous>)
    at ju.setVisible (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:1308:11760)

With this setup, I can now start the debugger. However, I'm still encountering a couple of issues:

1. Ctrl+Click navigation doesn't work: I can't jump to function definitions within my code using Ctrl+Click.
2. Container disconnection after ~2 hours of development, I'm getting disconnected from the container with the following error:

ENOPRO: No file system provider found for resource 'vscode-remote://dev-container%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-pipeline/forecasting/base_models/amazon_autopilot_model.py'

The only workaround I've found is to rebuild the container, which interrupts the workflow and isn’t ideal during active development.

Now, the errors in Developer Tools Console are:

log.ts:460   ERR UnboundLocalError: local variable 'end_index' referenced before assignment: Error: UnboundLocalError: local variable 'end_index' referenced before assignment
	at ae (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1962784)
	at oe (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1960744)
	at Immediate.<anonymous> (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1957038)
	at process.processImmediate (node:internal/timers:483:21)
log.ts:460   ERR _pickle.UnpicklingError: invalid load key, ' '.: Error: _pickle.UnpicklingError: invalid load key, ' '.
	at ae (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1962784)
	at oe (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1960744)
	at Immediate.<anonymous> (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1957038)
	at process.processImmediate (node:internal/timers:483:21)

Would appreciate any advice or suggestions on how to resolve these!

Thanks again.

[AlexandraDobrescu]

@rchiodo here it is the output I get if I am not adding Pylance in my .devcontainer.json file

mainThreadExtensionService.ts:78 [ms-python.python]Client is not running and can't be stopped. It's current state is: starting
$onExtensionRuntimeError @ mainThreadExtensionService.ts:78
mainThreadExtensionService.ts:79 Error: Client is not running and can't be stopped. It's current state is: starting
	at P.shutdown (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:2026065)
	at P.shutdown (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:2229122)
	at P.stop (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:2025637)
	at P.doInitialize (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:2025456)
	at async P.start (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:2022020)
	at async h.start (vscode-file://vscode-app/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:40228)
$onExtensionRuntimeError @ mainThreadExtensionService.ts:79
log.ts:460   ERR An unknown error occurred. Please consult the log for more details.
error @ log.ts:460
console.ts:137 [Extension Host] rejected promise not handled within 1 second: Error: Request initialize failed with message: You may install and use any number of copies of the software only with Microsoft Visual Studio, Visual Studio for Mac, Visual Studio Code, Azure DevOps, Team Foundation Server, and successor Microsoft products and services (collectively, the “Visual Studio Products and Services”) to develop and test your applications. The software is licensed, not sold. This agreement only gives you some rights to use the software. Microsoft reserves all other rights. You may not: work around any technical limitations in the software that only allow you to use it in certain ways; reverse engineer, decompile or disassemble the software, or otherwise attempt to derive the source code for the software, except and to the extent required by third party licensing terms governing use of certain open source components that may be included in the software; remove, minimize, block, or modify any notices of Microsoft or its suppliers in the software; use the software in any way that is against the law or to create or propagate malware; or share, publish, distribute, or lease the software (except for any distributable code, subject to the terms above), provide the software as a stand-alone offering for others to use, or transfer the software or this agreement to any third party.


dws @ console.ts:137
console.ts:137 [Extension Host] stack trace: Error: Request initialize failed with message: You may install and use any number of copies of the software only with Microsoft Visual Studio, Visual Studio for Mac, Visual Studio Code, Azure DevOps, Team Foundation Server, and successor Microsoft products and services (collectively, the “Visual Studio Products and Services”) to develop and test your applications. The software is licensed, not sold. This agreement only gives you some rights to use the software. Microsoft reserves all other rights. You may not: work around any technical limitations in the software that only allow you to use it in certain ways; reverse engineer, decompile or disassemble the software, or otherwise attempt to derive the source code for the software, except and to the extent required by third party licensing terms governing use of certain open source components that may be included in the software; remove, minimize, block, or modify any notices of Microsoft or its suppliers in the software; use the software in any way that is against the law or to create or propagate malware; or share, publish, distribute, or lease the software (except for any distributable code, subject to the terms above), provide the software as a stand-alone offering for others to use, or transfer the software or this agreement to any third party.


	at ae (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1962784)
	at oe (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1960744)
	at Immediate.<anonymous> (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1957038)
	at process.processImmediate (node:internal/timers:483:21)
dws @ console.ts:137
mainThreadExtensionService.ts:78 [ms-python.python]Request initialize failed with message: You may install and use any number of copies of the software only with Microsoft Visual Studio, Visual Studio for Mac, Visual Studio Code, Azure DevOps, Team Foundation Server, and successor Microsoft products and services (collectively, the “Visual Studio Products and Services”) to develop and test your applications. The software is licensed, not sold. This agreement only gives you some rights to use the software. Microsoft reserves all other rights. You may not: work around any technical limitations in the software that only allow you to use it in certain ways; reverse engineer, decompile or disassemble the software, or otherwise attempt to derive the source code for the software, except and to the extent required by third party licensing terms governing use of certain open source components that may be included in the software; remove, minimize, block, or modify any notices of Microsoft or its suppliers in the software; use the software in any way that is against the law or to create or propagate malware; or share, publish, distribute, or lease the software (except for any distributable code, subject to the terms above), provide the software as a stand-alone offering for others to use, or transfer the software or this agreement to any third party.


$onExtensionRuntimeError @ mainThreadExtensionService.ts:78
mainThreadExtensionService.ts:79 Error: Request initialize failed with message: You may install and use any number of copies of the software only with Microsoft Visual Studio, Visual Studio for Mac, Visual Studio Code, Azure DevOps, Team Foundation Server, and successor Microsoft products and services (collectively, the “Visual Studio Products and Services”) to develop and test your applications. The software is licensed, not sold. This agreement only gives you some rights to use the software. Microsoft reserves all other rights. You may not: work around any technical limitations in the software that only allow you to use it in certain ways; reverse engineer, decompile or disassemble the software, or otherwise attempt to derive the source code for the software, except and to the extent required by third party licensing terms governing use of certain open source components that may be included in the software; remove, minimize, block, or modify any notices of Microsoft or its suppliers in the software; use the software in any way that is against the law or to create or propagate malware; or share, publish, distribute, or lease the software (except for any distributable code, subject to the terms above), provide the software as a stand-alone offering for others to use, or transfer the software or this agreement to any third party.


	at ae (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1962784)
	at oe (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1960744)
	at Immediate.<anonymous> (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1957038)
	at process.processImmediate (node:internal/timers:483:21)
$onExtensionRuntimeError @ mainThreadExtensionService.ts:79

[karthiknadig]

@rchiodo the error in the last comment seems to be about the licensing.

[rchiodo]

@AlexandraDobrescu what version of VS code are you running? That license error would show up if you're not using the official VS code release.

[AlexandraDobrescu]

@rchiodo it is the 1.100.2 VSCode version

[rchiodo]

That should be supported. Maybe it's a red herring. The real problem is the Python extension not loading. Python debugger not working would indicate the Python extension didn't load.

[AlexandraDobrescu]

That makes sense, @rchiodo. Do you have any suggestions on how to fix the Python extension not loading?

[rchiodo]

This sounds like the error to me:

log.ts:460   ERR UnboundLocalError: local variable 'end_index' referenced before assignment: Error: UnboundLocalError: local variable 'end_index' referenced before assignment
	at ae (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1962784)
	at oe (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1960744)
	at Immediate.<anonymous> (/root/.vscode-server/extensions/ms-python.python-2025.6.1/out/client/extension.js:2:1957038)
	at process.processImmediate (node:internal/timers:483:21)

Not sure where that is in the python extension source, but it should be fixable in the Python extension's code.