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Pdb loops endlessly on non-interactive scripts #100141

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Pdb loops endlessly on non-interactive scripts#100141
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stdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@nphilipp
nphilipp
opened on Dec 9, 2022

Bug report

Pdb (as of 3.11.0, 3.11.1 and main branch, run from the command line) loops endlessly on non-interactive scripts.

To reproduce, run python -m pdb /dev/null from the command line. This loops, endlessly printing The program finished and will be restarted to the terminal. Pressing Ctrl + C drops you into the debugger shell, but entering quit only drops you back into that endless loop, I had to kill the process directly to make it quit.

With Python 3.10, it looks like this:

nils@makake:~> python3.10 -m pdb /dev/null
> /dev/null(1)<module>()
(Pdb) quit
nils@makake:~> python3.10 -m pdb -c c /dev/null
The program finished and will be restarted
> /dev/null(1)<module>()
(Pdb) q
nils@makake:~>

Your environment

  • CPython versions tested on: 3.11.0, 3.11.1, built from current main branch
  • Operating system and architecture: Fedora Linux 37, x86_64

Linked PRs

Activity

  1. nphilipp
    added
    type-bugAn unexpected behavior, bug, or error
    on Dec 9, 2022

  2. SnoopJ commented on Dec 9, 2022

    @SnoopJ
    SnoopJ
    on Dec 9, 2022
    Contributor

    Pressing Ctrl + C drops you into the debugger shell, but entering quit only drops you back into that endless loop, I had to kill the process directly to make it quit.

    I believe this happens because the keyboard interrupt puts you in post-mortem debugging mode, so the subsequent quit command does not apply to the original instance of Pdb, which continues its loop.

    This infinite loop also happens with an empty file or one containing no statements (but not "noninteractive scripts" that contain at least one statement), so the trace function that powers the debugger never fires. I'm not sure why/how the older versions started with a prompt even when no statements are present, though.

  3. SnoopJ commented on Dec 10, 2022

    @SnoopJ
    SnoopJ
    on Dec 10, 2022
    Contributor

    I've had a closer look at this, the change in behavior between 3.10 and 3.11 appears to be caused by #94552, although I don't really understand which part of pdb.py that's interacting with or how to resolve it.

  4. SonOfLilit
    added 2 commits that reference this issue on Jul 6, 2023

    Merge branch 'main' into pythongh-100141

    e5b1d00

    Merge branch 'main' into pythongh-100141

    6dffcb6

  5. SonOfLilit commented on Jul 8, 2023

    @SonOfLilit
    SonOfLilit
    on Jul 8, 2023

    I found the bug and wrote a PR, core dev feedback needed :-)

  6. iritkatriel
    added
    stdlibStandard Library Python modules in the Lib/ directory
    on Nov 26, 2023

  7. pelavarre commented on Sep 21, 2024

    @pelavarre
    pelavarre
    on Sep 21, 2024

    I found the Bug and wrote a PR, core dev feedback needed

    Do we know where this Bug is?

    Do we all know the test of: python3 -m pdb /dev/null
    still does hang some Python's today?

    Exact same cause as before, or a new escape, while none of us add this test?

    Three examples =>

    1 ) macOS latest fails this test

    % </dev/null python3 -m pdb /dev/null 2>&1 |head -3
The program finished and will be restarted
The program finished and will be restarted
The program finished and will be restarted
% 
% python3 --version                                
Python 3.12.6
% uname
Darwin
%

    Calling -m pdb to check Python Syntax hangs in this same way on a File of nothing but Comments and Line Breaks

    % cat p.py
#
% </dev/null python3 -m pdb p.py 2>&1 |head -3   
The program finished and will be restarted
The program finished and will be restarted
The program finished and will be restarted
%

    But go wander into the right corner of the Python world, and this problem does not repro out there. For example

    $ </dev/null python3 -m pdb /dev/null 2>&1 |head -3
> /dev/null(1)<module>()
(Pdb) 
$ 
$ python3 --version
Python 3.10.12
$ uname
Linux
$

    Am I helping? Can I help?

  8. pelavarre commented on Oct 12, 2024

    @pelavarre
    pelavarre
    on Oct 12, 2024

    Leaving this corner untested made it worse eventually

    Python 3.13 came out in Oct/2024, so I reran our tests there. I've now reported the process exit return code gone wrong on Syntax Error's, but also mentioned our infinite spam observations here, up now into

    "python3.13 -m pdb" exits zero on Syntax Error, prints infinite spam nearby
    #125367

    These corner weren't quite so broken till after Python 3.12

  9. picnixz commented on Oct 12, 2024

    @picnixz
    picnixz
    on Oct 12, 2024
    Member

    cc @gaogaotiantian as the pdb expert

  10. gaogaotiantian
    added a commit that references this issue on Oct 15, 2024

    gh-100141: Allow pdb to deal with empty file (#125425)

    bb9604b
  11. miss-islington
    added 2 commits that reference this issue on Oct 15, 2024

    pythongh-100141: Allow pdb to deal with empty file (pythonGH-125425)

    d192ba7

    pythongh-100141: Allow pdb to deal with empty file (pythonGH-125425)

    014c7aa

  12. gaogaotiantian commented on Oct 15, 2024

    @gaogaotiantian
    gaogaotiantian
    on Oct 15, 2024
    Member

    Fixed in #125425

  13. gaogaotiantian
    closed this as completedon Oct 15, 2024
  14. gaogaotiantian
    added 2 commits that reference this issue on Oct 15, 2024

    [3.13] gh-100141: Allow pdb to deal with empty file (GH-125425) (#125536

    6c79bae

    [3.12] gh-100141: Allow pdb to deal with empty file (GH-125425) (#125537

    90b1406
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