GeezerVison is showing github.com — gh-157170: Restore use_env() after test_use_prescr_screen in test_curses by iamsharduld · Pull Request #157171 · python/cpython
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iamsharduld
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Sep 8, 2026
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edited by bedevere-app
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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.
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…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.
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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.
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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
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Thanks for making the requested changes!
: please review the changes made to this pull request.
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This was referenced Sep 9, 2026
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⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️
Hi! The buildbot AMD64 Android 3.x (tier-3) has failed when building commit 5f14441.
What do you need to do:
- Don't panic.
- Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
- Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1591/builds/5200) and take a look at the build logs.
- Check if the failure is related to this commit (5f14441) or if it is a false positive.
- If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.
You can take a look at the buildbot page here:
https://buildbot.python.org/#/builders/1591/builds/5200
Summary of the results of the build (if available):
Click to see traceback logs
remote: Enumerating objects: 5, done.
remote: Counting objects: 25% (1/4)
remote: Counting objects: 50% (2/4)
remote: Counting objects: 75% (3/4)
remote: Counting objects: 100% (4/4)
remote: Counting objects: 100% (4/4), done.
remote: Compressing objects: 25% (1/4)
remote: Compressing objects: 50% (2/4)
remote: Compressing objects: 75% (3/4)
remote: Compressing objects: 100% (4/4)
remote: Compressing objects: 100% (4/4), done.
remote: Total 5 (delta 0), reused 0 (delta 0), pack-reused 1 (from 1)
From https://github.com/python/cpython
* branch main -> FETCH_HEAD
Note: switching to '5f14441114af4b8aadf45aa0dd764e43f5eedd5d'.
You are in 'detached HEAD' state. You can look around, make experimental
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Turn off this advice by setting config variable advice.detachedHead to false
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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curl: (22) The requested URL returned error: 500
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curl: (22) The requested URL returned error: 500
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curl: (22) The requested URL returned error: 500
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clin1234
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to clin1234/cpython
that referenced
this pull request
Sep 12, 2026
…st_curses (pythonGH-157171)
curses.use_env() sets a process-wide ncurses setting, not a property of
the screen it is called on.
johnslavik
pushed a commit
to johnslavik/cpython
that referenced
this pull request
Sep 14, 2026
…st_curses (pythonGH-157171)
curses.use_env() sets a process-wide ncurses setting, not a property of
the screen it is called on.
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