Python debugging, language server problem

Question

I'm having very repeatable problems running the Python debugger under VS code 1.74.2 on Mac OS 11.6. I decided to follow some advice in the repository's "reporting issues" article and turn off all extensions. Make that, all extensions except the ones obviously needed for the job. I turned off all extensions except the core Python extension, turning off PyLance and everything to do with Jupyter. Doesn't exactly help, my problem arises in a somewhat different form.

1. Properly, what is the minimal set of extensions needed to do Python debugging? Is it more than the core Python extension?

2. What exactly is a language server in this context? Could someone point me to documentation that will "take it from the top" and explain what this concept is all about?

3. I would appreciate some help interpreting what I'm seeing in log files and how to work with it. Looks like I'm seeing an actual bug in Python extension code, but I'd like another pair of eyes.

A representative sample from 1-Python.log:

[ERROR 2022-11-28 15:16:37.609]: [
  'Failed to start language server, Class name = h, completed in 1956ms, has a falsy return value, Arg 1: <Uri:/Users/ken/Shoshin/UI>, Arg 2: {"id":"/usr/local/bin/python3","sysPrefix":"/Library/Frameworks/Python.framework/Versions/3.9","envType":"Global","envName":"","envPath":"","path":"/usr/local/bin/python3","architecture":3,"sysVersion":"3.9.7 (v3.9.7:1016ef3790, Aug 30 2021, 16:39:15) \\n[Clang 6.0 (clang-600.0.57)]","version":{"raw":"3.9.7","major":3,"minor":9,"patch":7,"build":[],"prerelease":["final","0"]},"displayName":"Python 3.9.7 64-bit","detailedDisplayName":"Python 3.9.7 64-bit"}, Return Value: undefined',
  [Error: Launching Jedi language server using python failed, see output.
    at l.start (/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/out/client/extension.js:2:19756)]
]
[ERROR 2022-11-28 15:16:37.609]: [
  'Failed to activate a workspace, Class name = f, completed in 2036ms, has a falsy return value, Arg 1: <Uri:/Users/ken/Shoshin/UI/try/HelloWorld.py>, Return Value: undefined',
  [Error: Launching Jedi language server using python failed, see output.
    at l.start (/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/out/client/extension.js:2:19756)]
]
[ERROR 2022-11-28 15:16:37.609]: Failure during activation. [Error: Launching Jedi language server using python failed, see output.
    at l.start (/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/out/client/extension.js:2:19756)]
[ERROR 2022-11-28 15:16:37.609]: sendStartupTelemetry() failed. [Error: Launching Jedi language server using python failed, see output.
    at l.start (/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/out/client/extension.js:2:19756)]
DAP Server launched with command: /usr/local/bin/python3 /Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/lib/python/debugpy/adapter
DAP Server launched with command: /usr/local/bin/python3 /Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/lib/python/debugpy/adapter

Corresponding material from 3-Python language server.log:

Traceback (most recent call last):
  File "/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/run-jedi-language-server.py", line 11, in <module>
    sys.exit(cli())
  File "/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/lib/jedilsp/jedi_language_server/cli.py", line 125, in cli
    SERVER.start_io()
  File "/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/lib/jedilsp/pygls/server.py", line 225, in start_io
    self.loop.run_until_complete(
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "/Users/ken/.vscode/extensions/ms-python.python-2022.21.13491005/pythonFiles/lib/jedilsp/pygls/server.py", line 56, in aio_readline
    header = await loop.run_in_executor(executor, rfile.readline)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/base_events.py", line 814, in run_in_executor
    executor.submit(func, *args), loop=self)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/concurrent/futures/thread.py", line 170, in submit
    self._adjust_thread_count()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/concurrent/futures/thread.py", line 193, in _adjust_thread_count
    t.start()
TypeError: start() missing 1 required positional argument: 'sessionID'
[Error - 3:16:39 PM] The Python Jedi server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.
[Error - 3:16:39 PM] Server initialization failed.
  Message: Pending response rejected since connection got disposed
  Code: -32097 
[Error - 3:16:39 PM] Python Jedi client: couldn't create connection to server.
  Message: Pending response rejected since connection got disposed
  Code: -32097 
[Error - 3:16:39 PM] Restarting server failed
  Message: Pending response rejected since connection got disposed
  Code: -32097 

After switching to PyLance language server:

[Info  - 7:36:39 AM] (39856) Pylance language server 2022.12.20 (pyright 621d886b) starting
[Info  - 7:36:39 AM] (39856) Server root directory: /Users/ken/.vscode/extensions/ms-python.vscode-pylance-2022.12.20/dist
[Info  - 7:36:39 AM] (39856) Starting service instance "UI"
[Info  - 7:36:39 AM] (39856) Notebook support: Legacy
[Info  - 7:36:39 AM] (39856) Interactive window support: Legacy
[Info  - 7:36:39 AM] (39856) Auto-indent enabled
[Info  - 7:36:39 AM] (39856) No configuration file found.
[Info  - 7:36:39 AM] (39856) No pyproject.toml file found.
[Info  - 7:36:39 AM] (39856) Setting pythonPath for service "UI": "/usr/local/bin/python3"
[Warn  - 7:36:39 AM] (39856) stubPath /Users/ken/Shoshin/UI/typings is not a valid directory.
[Info  - 7:36:39 AM] (39856) Assuming Python version 3.9
[Info  - 7:36:39 AM] (39856) Assuming Python platform Darwin
[Info  - 7:36:39 AM] (39856) Searching for source files
[Info  - 7:36:39 AM] (39856) Found 61 source files
[Info  - 7:36:39 AM] (39856) Background analysis(1) root directory: /Users/ken/.vscode/extensions/ms-python.vscode-pylance-2022.12.20/dist
[Info  - 7:36:39 AM] (39856) Background analysis(1) started
[Info  - 7:44:45 AM] (39856) Indexer background runner(2) root directory: /Users/ken/.vscode/extensions/ms-python.vscode-pylance-2022.12.20/dist (index)
[Info  - 7:44:45 AM] (39856) Indexing(2) started
[Info  - 7:44:45 AM] (39856) scanned(2) 238 files over 1 exec env
[Info  - 7:44:48 AM] (39856) [IDX(2)] Long operation: index execution environment /Users/ken/Shoshin/UI (2240ms)
[Info  - 7:44:48 AM] (39856) [IDX(2)] Long operation: index packages /Users/ken/Shoshin/UI (2243ms)
[Info  - 7:44:48 AM] (39856) indexed(2) 154 files over 1 exec env
[Info  - 7:44:48 AM] (39856) Indexing finished(2).

Answer 1

what is the minimal set of extensions needed to do Python debugging?

It is the Python extensions. This extension includes everything you need to write, run, and debug Python code, including a language server.

It seems in your logs that there may be a problem with the Jedi language server. Modify the python.languageServer configuration to pylance.

    "python.languageServer": "Pylance",