Crash on start when debug Python 3.14t.rc02

[Honghe]

Environment data

• debugpy version: 1.8.16
• OS and version: windows 11
• Python version: conda-forge python 3.14.rc02 free-threaded
• Using VS Code or Visual Studio: vscode

Actual behavior

vscode debug crash on start:

>  & 'c:\Users\x\miniforge3\envs\py314t\python.exe' 'c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.10.0-win32-x64\bundled\libs\debugpy\launcher' '63765' '--' 'E:\pythonprojects\uv_py314t\csp.py' 
Traceback (most recent call last):
  File "c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.10.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_sys_monitoring\_pydevd_sys_monitoring.py", line 876, in _unwind_event
    if not thread_info.trace or not thread_info.is_thread_alive():
  File "c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.10.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_sys_monitoring\_pydevd_sys_monitoring.py", line 270, in is_thread_alive
    return not self.thread._handle.is_done()
AttributeError: '_MainThread' object has no attribute '_handle'

Expected behavior

It can debug the following code.

Steps to reproduce:

debug the following code:

from concurrent import interpreters

interp = interpreters.create()

def run(q):
    print("before arg")
    print(q.get())

q = interpreters.create_queue()
t = interp.call_in_thread(run, q)
q.put("Hello from the main thread!")
t.join()

[rchiodo]

That version of the debugger extension is not using the debugpy 1.8.16. It's still on 1.8.13.

If you upgrade the ms-python.vsdebug extension to the insider's version, it should work with 3.14.

[Honghe]

That version of the debugger extension is not using the debugpy 1.8.16. It's still on 1.8.13.

If you upgrade the ms-python.vsdebug extension to the insider's version, it should work with 3.14.

After upgrade ms-python.vsdebug to 2025.11.2025072901， it still doesn't work.

>'c:\Users\x\miniforge3\envs\py314t\python.exe' 'c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.11.2025072901-win32-x64\bundled\libs\debugpy\launcher' '49673' '--' 'E:\pythonprojects\demo_python314\csp.py' 
Traceback (most recent call last):
  File "c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.11.2025072901-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_sys_monitoring\_pydevd_sys_monitoring.py", line 876, in _unwind_event
    if not thread_info.trace or not thread_info.is_thread_alive():
  File "c:\Users\x\.vscode\extensions\ms-python.debugpy-2025.11.2025072901-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_sys_monitoring\_pydevd_sys_monitoring.py", line 270, in is_thread_alive
    return not self.thread._handle.is_done()
AttributeError: '_MainThread' object has no attribute '_handle'

[rchiodo]

Oh it seems that's still on 1.8.13. Not sure when they're going to update. But that's the root cause of the bug.

[rchiodo]

There is a temporary workaround that you can use until the debugger extension updates. Put this in your launch.json:

     "debugAdapterPath": "<path to debugpy>\\src\\debugpy\\adapter"

And pip install debugpy

[rchiodo]

When this commit ships:
microsoft/vscode-python-debugger@b748cb8

The extension should have the latest version.

[Honghe]

There is a temporary workaround that you can use until the debugger extension updates. Put this in your launch.json:

 "debugAdapterPath": "<path to debugpy>\\src\\debugpy\\adapter"

And pip install debugpy

It works, thanks.
How to inspec the running debugpy version of ms-python-debug extension except checking the static debugpy_info.json file?

[rchiodo]

You can print the debugpy version:

import debugpy
print(debugpy.__version__)

Either in code or in the debug console.