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IDLE restarts when one debugs code raising SystemExit #71136

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IDLE restarts when one debugs code raising SystemExit#71136
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topic-IDLEtype-bugAn unexpected behavior, bug, or error

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@pppery
pppery
mannequin
opened on May 4, 2016
BPO 26949
Nosy @terryjreedy, @pppery, @mlouielu
PRs
  • gh-71136: IDLE: Fix hanging when raise KeyboardInterrupt with debugger open #1711
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = None
created_at = <Date 2016-05-04.12:49:03.499>
labels = ['expert-IDLE', 'type-bug', '3.9']
title = 'IDLE restarts when one debugs code raising SystemExit'
updated_at = <Date 2019-09-20.20:57:18.028>
user = 'https://github.com/pppery'

    bugs.python.org fields:

    activity = <Date 2019-09-20.20:57:18.028>
actor = 'terry.reedy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2016-05-04.12:49:03.499>
creator = 'ppperry'
dependencies = []
files = []
hgrepos = []
issue_num = 26949
keywords = []
message_count = 9.0
messages = ['264861', '264863', '264867', '265097', '265101', '294124', '294125', '294775', '352889']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'ppperry', 'louielu']
pr_nums = ['1711']
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26949'
versions = ['Python 3.9']

    Linked PRs

    Activity

    1. pppery
      added
      topic-IDLE
      type-bugAn unexpected behavior, bug, or error
      on May 4, 2016

    2. terryjreedy commented on May 4, 2016

      @terryjreedy
      terryjreedy
      on May 4, 2016
      Member

      To be more specific: if one runs a file, the shell is restarted (with the file name). In the file, raise SystemExit is normally the same as running off the end of the file, and a prompt is printed. If one runs a file with debugger on, [DEBUG ON] is printed before the prompt. However, SystemExit while debugging causes a Restart Shell before the [DEBUG ON] and >>> prompt. The 2nd restart does not normally happen when debugging finishes. It does not happen when any other exception is raised; instead a traceback is printed as normal.

      This is a minor bug, but it does prevent interactive examination of the process after debugging.

      There is special code in run.py to catch SystemExit and not print a traceback. My guess in a bug in RemoteDebugger.py that causes (allows) the execution process to exit or otherwise get detached from the IDLE process. When the IDLE process loses contact with the current execution process, it starts a new one.

    3. pppery commented on May 4, 2016

      @pppery
      ppperymannequin
      on May 4, 2016
      MannequinAuthor

      Terry, Your how to reproduce is more complicated than necessary. This bug can be reproduced by just turning on the debugger in a python shell and typing raise SystemExit then pressing step in the debugger.

    4. terryjreedy commented on May 5, 2016

      @terryjreedy
      terryjreedy
      on May 5, 2016
      Member

      Thanks, that may make debugging this (and creating a test) easier. I have only seriously used debugger with files, and often with breakpoints in the file.

    5. pppery commented on May 7, 2016

      @pppery
      ppperymannequin
      on May 7, 2016
      MannequinAuthor

      This issue has worse consequences than I previously thought. It also affects KeyboardInterrupt with worse consequences.

      If you run a program raising KeyboardInterrupt in the debugger, the shell will hang. Restarting the shell fixes this problem.

    6. terryjreedy commented on May 7, 2016

      @terryjreedy
      terryjreedy
      on May 7, 2016
      Member

      bpo-14111 is about handling ^C while debugging. So for now I will assume that handling 'raise KeyboardInterrupt' is part of that issue.

    7. mlouielu commented on May 22, 2017

      @mlouielu
      mlouielumannequin
      on May 22, 2017
      Mannequin

      The problem is cause by run.py:main function, when it catch KeyboardInterrupt or SystemExit, it won't put a blank msg back to response_queue, that cause the loop in run.py:main triggering except queue.Empty to continue the loop.

      So, I think the KeyboardInterrupt hang is a bug, cause by the infinity loop above, but SystemExit will raise SystemExit again, and break down the loop, let the shell restart. I think this isn't a bug.

      Let's say there is a code like this:

          x = 10
    print(x)
    raise SystemExit
    print(x)

      When using IDLE to run this file without debugger, it will print 10 and leave below code. But when you type "x" in the shell, it will pop up 10, that means the shell environment didn't exit, still exist inside.

      But if you open the debugger, let SystemExit break the loop and restart the shell, I think this is a normal behavior -- that it should exit the shell (and restart it)

    8. mlouielu commented on May 22, 2017

      @mlouielu
      mlouielumannequin
      on May 22, 2017
      Mannequin

      PR 1711 fix KeyboardInterrupt with adding rpc.repsonse_queue.put, but it will not print out the exception traceback.

      And for SystemExit, wait for discussion result.

    9. terryjreedy commented on May 30, 2017

      @terryjreedy
      terryjreedy
      on May 30, 2017
      Member

      Louie> If you run your example in Python with -i, you will see the same behavior, except for the traceback, as with IDLE.

      F:\dev\cpython>python -i -c "x=10; print(x); raise SystemExit"
Running Debug|Win32 interpreter...
10
Traceback (most recent call last):
  File "<string>", line 1, in <module>
SystemExit
>>> x
10

      Ditto for "python -i testfile.py". I would like the behavior to be the same when debugging.

    10. terryjreedy commented on Sep 20, 2019

      @terryjreedy
      terryjreedy
      on Sep 20, 2019
      Member

      >> raise SystemExit does not normally cause a restart.

    11. terryjreedy
      added
      3.9 (EOL)end of life
      on Sep 20, 2019
    12. ezio-melotti
      transferred this issue fromon Apr 10, 2022
    13. terryjreedy
      added this to IDLE Issueson Jul 23, 2022
    14. erlend-aasland
      moved this to In Progress in IDLE Issueson Jul 27, 2022
    15. picnixz
      added
      stdlibStandard Library Python modules in the Lib/ directory
      and removed
      3.9 (EOL)end of life
      on Nov 10, 2025
    16. terryjreedy
      removed
      stdlibStandard Library Python modules in the Lib/ directory
      on Jan 15, 2026

    17. serhiy-storchaka commented on Sep 15, 2026

      @serhiy-storchaka
      serhiy-storchaka
      on Sep 15, 2026
      Member

      Both halves have the same cause: code run under the debugger bypasses Executive.runcode(), so its exceptions escape to the request loop in run.main(), which dropped a KeyboardInterrupt without replying (hang) and re-raises a SystemExit (restart). #157566 fixes the hang; the restart can be done separately.

    18. terryjreedy
      added 3 commits that reference this issue on Sep 26, 2026

      gh-71136: Fix IDLE Shell hang after KeyboardInterrupt under the debug…

      ee1bbf0

      [3.13] gh-71136: Fix IDLE Shell hang after KeyboardInterrupt under th…

      ca42f6a

      [3.14] gh-71136: Fix IDLE Shell hang after KeyboardInterrupt under th…

      1ef709e

    19. terryjreedy commented on Sep 26, 2026

      @terryjreedy
      terryjreedy
      on Sep 26, 2026
      Member

      'raise KeyboardInterrupt' in debugged code should be fixed. I changed the IDLE issues topic from Restart to Debugger. I hope someday to consider Debugger issues as a group and then include this minor issue of how 'raise SystemExit' in debugged code behaves.

    20. terryjreedy
      added a commit that references this issue on Oct 9, 2026

      [3.15] gh-71136: Fix IDLE Shell hang after KeyboardInterrupt under th…

      e70fbd3
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