gh-71136: IDLE: Fix hanging when raise KeyboardInterrupt with debugger open

[mlouielu]

When catch KeyboardInterrupt, it should put a dummy msg back to response_queue to prevent queue.Empty cause the infinity loop.

https://bugs.python.org/issue26949

• Issue: IDLE restarts when one debugs code raising SystemExit #71136

[mention-bot]

@mlouielu, thanks for your PR! By analyzing the history of the files in this pull request, we identified @kbkaiser, @terryjreedy and @asvetlov to be potential reviewers.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[auvipy]

I'm not sure, should we rework on this or close this completely?

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[josephholsten]

My results are:

• gh-71136: IDLE: Fix hanging when raise KeyboardInterrupt with debugger open #1711 rebases clean and seems fine, see gh-71136: IDLE: Fix hanging when raise KeyboardInterrupt with debugger open #141328
• https://bugs.python.org/issue14111 reproduction steps still seem to occur. Specifically:

The reproduce step can be reduce to:

1. open idlelib with debugger (./python -m idlelib -d)
2. enter print() (or any other function call)
3. Control-C breakout

Then it will restart the shell.

Yields:

Python 3.14.0 (main, Oct  7 2025, 09:34:52) [Clang 17.0.0 (clang-1700.0.13.3)] on darwin
Enter "help" below or click "Help" above for more information.
[DEBUG ON]
print()

================================ RESTART: Shell ================================
[DEBUG ON]