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Exact reporting of curses C function failures #133579

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Exact reporting of curses C function failures#133579
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picnixz
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extension-modulesC modules in the Modules dirtype-bugAn unexpected behavior, bug, or error

Description

@picnixz
picnixz
opened on May 7, 2025

When calling some curses C functions, we ignore their return values. Those are:

  • in PyCursesWindow_dealloc, we ignore delwin() errors

  • in _curses_initscr_impl, we ignore wrefresh() errors

  • in _curses_window_addstr_impl, we ignore wattrset() errors and prefer reporting errors due to adding strings. Same for the insstr* functions

  • in _curses_window_box_impl, we ignore the error returned by box(). This is correct because the manual says (for box):

    All routines return the integer OK. The SVr4.0 manual says "or a non-negative integer if immedok is set", but this appears to be an error. X/Open does not define any error conditions. This implementation returns an error if the window pointer is null.

    In this case, I think it's better to explicitly suppress the return value and link the manpage.

The question now is:

  • What should we do for a failing delwin() in the destructor?
  • What should we do for wattrset() when this routine is not the "important" one?

cc @encukou

Note

We will not backport these fixes as they could break existing code that could be surprised by a new exception.

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Activity

  1. picnixz
    self-assigned this
    on May 7, 2025
  2. picnixz
    added
    type-featureA feature request or enhancement
    extension-modulesC modules in the Modules dir
    on May 7, 2025
  3. picnixz
    added this to Curses issueson May 7, 2025

  4. encukou commented on May 17, 2025

    @encukou
    encukou
    on May 17, 2025
    Member

    What should we do for a failing delwin() in the destructor?

    Set an exception and call PyErr_WriteUnraisable, so that it's caught by unraisablehook.

    What should we do for wattrset() when this routine is not the "important" one?

    In _curses_window_addstr_impl, wattrset is only called if the user explicitly called addstr with an attr argument. Failure to set them should be a hard error, to be handled by the user.

    _curses_window_box_impl

    IMO, if an error is reported, something is wrong and we should raise an exception.

    IMO, these would be bugfixes, but should not be backported.

  5. picnixz
    added
    type-bugAn unexpected behavior, bug, or error
    triagedThe issue has been accepted as valid by a triager.
    and removed
    type-featureA feature request or enhancement
    triagedThe issue has been accepted as valid by a triager.
    on May 18, 2025

  6. picnixz commented on May 18, 2025

    @picnixz
    picnixz
    on May 18, 2025
    MemberAuthor

    Thanks. I've found other occurrences where curses C functions are called but the error handling is not done. It's just that it was sometimes under ifdef that I missed. I need #125844 to be merged first so that I can use the helpers out there so I'm holding this work for now.

  7. picnixz commented on May 19, 2025

    @picnixz
    picnixz
    on May 19, 2025
    MemberAuthor

    On failure, _curses.window.getstr also return an empty string instead of reporting the error. It may be fine, but I don't know if it wouldn't be better to actually report the possible error.

  8. picnixz
    added a commit that references this issue on May 27, 2025

    gh-133579: consistently report C curses function failures (#134327)

    30dde1e
  9. picnixz
    added a commit that references this issue on Jun 8, 2025

    gh-133579: correctly report C curses errors in `_curses_panel` (#134629)

    d610f11
  10. picnixz
    closed this as completedon Jun 8, 2025
  11. github-project-automation
    moved this to Done in Curses issueson Jun 8, 2025
  12. lkollar
    added a commit that references this issue on Jun 19, 2025

    pythongh-133579: correctly report C curses errors in `_curses_panel` (p…

    9171a96
  13. Pranjal095
    added 2 commits that reference this issue on Jul 12, 2025

    pythongh-133579: consistently report C curses function failures (pyth…

    1a7b413

    pythongh-133579: correctly report C curses errors in `_curses_panel` (p…

    f4277e3
  14. taegyunkim
    added 2 commits that reference this issue on Aug 4, 2025

    pythongh-133579: consistently report C curses function failures (pyth…

    770a3bf

    pythongh-133579: correctly report C curses errors in `_curses_panel` (p…

    bf1c3fa
  15. Agent-Hellboy
    added a commit that references this issue on Aug 19, 2025

    pythongh-133579: correctly report C curses errors in `_curses_panel` (p…

    40b40ad
  16. gostak-dd
    added a commit that references this issue on Jun 2, 2026

    pythongh-133579: consistently report C curses function failures (pyth…

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