gh-157170: Restore use_env() after test_use_prescr_screen in test_curses by iamsharduld · Pull Request #157171 · python/cpython · GitHub

test_use_prescr_screen turns use_env off to show that a new_prescr() screen can be used to affect state before initscr(), and never turns it back on. curses.use_env() calls ncurses' use_env(), which sets the process-wide default (_nc_prescreen.use_env) that every later screen copies, not a property of the screen that is current at the time. With it off, ncurses sizes a screen from the terminfo lines/cols capabilities alone, and the linux entry used by the CI runners has none, so every newterm() for the rest of the process returns NULL. That is the 138 errors test_curses reports in the parallel phase of every Ubuntu CI run (all 31 Ubuntu job runs in the last 8 successful runs on main); the sequential rerun passes only because it re-runs the failed tests by name and so never runs ScreenTests first. Details, including an ncurses trace of the failing newterm(), are in the issue.

This restores the setting with addCleanup(). Verified on Ubuntu 25.10 with ncurses 6.5 (the newterm-based setUp() needs ncurses 6.5 or newer):

TERM=linux ./python -m test test_curses -u curses: 138 errors before, passes after (three consecutive runs).
TERM=linux ./python -m test --fast-ci test_curses: no rerun needed after.
TERM=xterm still passes.

On macOS the ScreenTests are skipped (ncurses 6.0), which is why this was invisible on developer machines.

Issue: test_curses fails in every Ubuntu CI run's parallel phase: test_use_prescr_screen leaves use_env(False) set, so newterm() fails with TERM=linux #157170

…st_curses curses.use_env() sets a process-wide ncurses default, not a property of the screen it is called on. test_use_prescr_screen turned it off and never turned it back on, so every newterm() in the rest of the process took the screen size from terminfo alone. For a terminfo entry with no size, such as "linux" on the CI runners, that makes newterm() return NULL: test_curses failed with 138 errors in the parallel phase of every Ubuntu CI run and only passed on the rerun, which skips ScreenTests.

Good catch, and thank you for the trace.

Please drop the NEWS entry. This is a fix to unreleased test. It does not need a NEWS entry.

Please simplify the comment, it is too verbose. One addition line would be enough.

Thank you. Both done in a779f46:

NEWS entry dropped. bedevere/news will stay red until skip news is applied.
The comment is now a single line: # use_env() is process-wide, not a property of this screen.

The diff is two added lines. Re-ran test_curses with TERM=linux and with TERM=xterm-256color; both pass.

I have made the requested changes; please review again

Thanks for making the requested changes!

: please review the changes made to this pull request.

LGTM. 👍

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remote: Enumerating objects: 5, done.        
remote: Counting objects:  25% (1/4)        
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remote: Counting objects:  75% (3/4)        
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remote: Counting objects: 100% (4/4), done.        
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remote: Total 5 (delta 0), reused 0 (delta 0), pack-reused 1 (from 1)        
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HEAD is now at 5f14441114a gh-157170: Restore use_env() after test_use_prescr_screen in test_curses (GH-157171)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdec found; falling back to pure-Python version for the decimal module

../../Parser/lexer/string.c: In function ‘finish_ftstring_expr’:
../../Parser/lexer/string.c:81:20: warning: variable ‘previous_end’ set but not used [-Wunused-but-set-variable]
   81 |         _PyTok_Off previous_end = state->expr_span.start;
      |                    ^~~~~~~~~~~~
In file included from ../../Include/internal/pycore_dict.h:11,
                 from ../../Objects/typeobject.c:8:
In function ‘Py_DECREF_MORTAL’,
    inlined from ‘PyStackRef_CLOSE’ at ../../Include/internal/pycore_stackref.h:703:9,
    inlined from ‘_PyThreadState_PopCStackRef’ at ../../Include/internal/pycore_stackref.h:811:5,
    inlined from ‘vectorcall_maybe’ at ../../Objects/typeobject.c:3118:9:
../../Include/internal/pycore_object.h:448:8: warning: array subscript 0 is outside array bounds of ‘PyObject[0]’ {aka ‘struct _object[]’} [-Warray-bounds]
  448 |     if (--op->ob_refcnt == 0) {
      |        ^

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* main: (158 commits) pythongh-156924: Try reifying lazy imports in `ForwarRef.evaluate()` (python#156940) pythongh-156233: Fix typos and code snippet errors in the docs (python#156475) pythongh-156837: Refer to yield expressions in generator function definitions (pythonGH-156863) pythongh-155292: Skip updating unicodedata with mismatched interpreter (pythonGH-157066) pythongh-157170: Document the scope of global curses settings (pythonGH-157207) pythongh-155966: Correct handling of `math.tanpi` poles (python#155980) pythongh-157170: Restore use_env() after test_use_prescr_screen in test_curses (pythonGH-157171) pythongh-156910: fix deadlock in type_set_abstractmethods under free-threading (python#156948) pythongh-155648: Write the empty and placeholder IDLE tests (python#156260) pythongh-153569: centralize formatted-string state and source spans (python#156484) pythongh-157137: Mark the PEP 820 soft deprecations as 3.15, not `next` (python#157138) pythongh-152433: Use regular LoadLibrary in UWP for Windows system libs (pythonGH-156972) pythongh-121617: Fix Py_CLEAR() memcpy in C++: replace NULL with _Py_NULL (python#157188) pythongh-157135: Fix documentation errors in the `math.atan{2}pi` functions (python#157136) pythongh-121617: Fix Py_CLEAR() in C++: replace NULL with _Py_NULL (python#157067) pythongh-156774: Speed up pdb startup with asyncio guard (python#156775) pythongh-156109: Allow static, non-framework iOS builds (python#156110) pythongh-156780: Emscripten: add missing EM_JS_DEPS (python#156798) pythongh-152936: Make privileged functions available on Android (python#152977) pythongh-123018: Keep the libedit history file header when truncating (pythonGH-157165) ...

…st_curses (pythonGH-157171) curses.use_env() sets a process-wide ncurses setting, not a property of the screen it is called on.

bedevere-app Bot mentioned this pull request Sep 8, 2026

test_curses fails in every Ubuntu CI run's parallel phase: test_use_prescr_screen leaves use_env(False) set, so newterm() fails with TERM=linux #157170

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bedevere-app Bot added tests Tests in the Lib/test dir awaiting review labels Sep 8, 2026

iamsharduld mentioned this pull request Sep 8, 2026

gh-157184: Scale the join() alarm in the multiprocessing kill tests #157185

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serhiy-storchaka self-requested a review September 9, 2026 07:49

serhiy-storchaka added the skip news label Sep 9, 2026

serhiy-storchaka reviewed Sep 9, 2026

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Address review: drop the NEWS entry and shorten the comment

a779f46

bedevere-app Bot added awaiting change review and removed awaiting review labels Sep 9, 2026

This was referenced Sep 9, 2026

gh-131178: Add tests for pstats command-line interface #157133

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gh-131178: Add tests for ensurepip command-line interface #157154

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gh-157161: Fix test_rollover_based_on_st_birthtime_only on slow machines #157162

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serhiy-storchaka approved these changes Sep 9, 2026

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bedevere-app Bot added awaiting merge and removed awaiting change review labels Sep 9, 2026

serhiy-storchaka merged commit 5f14441 into python:main Sep 9, 2026
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bedevere-app Bot removed the awaiting merge label Sep 9, 2026

gh-157170: Restore use_env() after test_use_prescr_screen in test_curses by iamsharduld · Pull Request #157171 · python/cpython · GitHub

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gh-157170: Restore use_env() after test_use_prescr_screen in test_curses - #157171

gh-157170: Restore use_env() after test_use_prescr_screen in test_curses#157171
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iamsharduld:fix-curses-use-env-cleanup

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gh-157170: Restore use_env() after test_use_prescr_screen in test_curses by iamsharduld · Pull Request #157171 · python/cpython · GitHub

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gh-157170: Restore use_env() after test_use_prescr_screen in test_curses - #157171

gh-157170: Restore use_env() after test_use_prescr_screen in test_curses#157171serhiy-storchaka merged 2 commits intopython:mainpython/cpython:mainfrom iamsharduld:fix-curses-use-env-cleanupiamsharduld/cpython:fix-curses-use-env-cleanupCopy head branch name to clipboard

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gh-157170: Restore use_env() after test_use_prescr_screen in test_curses#157171
serhiy-storchaka merged 2 commits into
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iamsharduld:fix-curses-use-env-cleanup

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