gh-155974: Restore the window attributes when a curses write fails (GH-155975)

https://github.com/python/cpython/commit/83531fd39f24f873671c38b981061afe1730613f
commit: 83531fd39f24f873671c38b981061afe1730613f
branch: main
author: Vyron Vasileiadis <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-08-20T22:08:50+03:00
summary:

gh-155974: Restore the window attributes when a curses write fails (GH-155975)

addstr(), addnstr(), insstr() and insnstr() set the window rendition to
the caller's attr, write, then restore the previous rendition.  Since
30dde1eeb3fa the restore sits below an early return taken when the write
fails, so a failed write leaves the caller's attr on the window and
drops whatever the application had set with attrset().

Restore the rendition first and report the write error afterwards.  A
wattrset() failure is still reported when the write itself succeeded.

files:
A Misc/NEWS.d/next/Library/2026-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst
M Lib/test/test_curses.py
M Modules/_cursesmodule.c

diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index f582336fae1734..6ab951ad2786ea 100644
--- a/Lib/test/test_curses.py
+++ b/Lib/test/test_curses.py
@@ -895,6 +895,21 @@ def test_output_string_embedded_null_chars(self):
                 self.assertRaises(ValueError, stdscr.insstr, arg)
                 self.assertRaises(ValueError, stdscr.insnstr, arg, 1)
 
+    def test_output_string_attr_restored(self):
+        # A write with an attr restores the window rendition afterwards,
+        # whether it succeeded or failed.
+        win = curses.newwin(2, 10, 0, 0)
+        for func, args in [(win.addstr, ('x',)), (win.addnstr, ('x', 1)),
+                           (win.insstr, ('x',)), (win.insnstr, ('x', 1))]:
+            with self.subTest(func.__qualname__):
+                win.attrset(curses.A_UNDERLINE)
+                # y=100 is outside the window, so the write fails.
+                self.assertRaises(curses.error, func, 100, 0, *args,
+                                  curses.A_BOLD)
+                self.assertEqual(win.getattrs(), curses.A_UNDERLINE)
+                func(0, 0, *args, curses.A_BOLD)
+                self.assertEqual(win.getattrs(), curses.A_UNDERLINE)
+
     def test_add_string_behavior(self):
         # addstr() advances the cursor past the written text; addnstr()
         # writes at most n characters.
diff --git a/Misc/NEWS.d/next/Library/2026-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst b/Misc/NEWS.d/next/Library/2026-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst
new file mode 100644
index 00000000000000..8621bc49a03cca
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst
@@ -0,0 +1,4 @@
+Fix a regression in Python 3.15: :meth:`~curses.window.addstr`,
+:meth:`~curses.window.addnstr`, :meth:`~curses.window.insstr` and
+:meth:`~curses.window.insnstr` again restore the window attributes when the
+write fails, instead of leaving the temporary *attr* applied.
diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 006e27d55d8925..0bab30184a357a 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -2262,15 +2262,14 @@ _curses_window_addstr_impl(PyCursesWindowObject *self, int group_left_1,
         }
         Py_DECREF(bytesobj);
     }
-    if (rtn == ERR) {
-        curses_window_set_error(self, funcname, "addstr");
-        return NULL;
-    }
     if (use_attr) {
-        rtn = wattrset(self->win, attr_old);
-        return curses_window_check_err(self, rtn, "wattrset", "addstr");
+        int attr_rtn = wattrset(self->win, attr_old);
+        if (rtn != ERR) {
+            rtn = attr_rtn;
+            funcname = "wattrset";
+        }
     }
-    Py_RETURN_NONE;
+    return curses_window_check_err(self, rtn, funcname, "addstr");
 }
 
 /*[clinic input]
@@ -2373,15 +2372,14 @@ _curses_window_addnstr_impl(PyCursesWindowObject *self, int group_left_1,
         }
         Py_DECREF(bytesobj);
     }
-    if (rtn == ERR) {
-        curses_window_set_error(self, funcname, "addnstr");
-        return NULL;
-    }
     if (use_attr) {
-        rtn = wattrset(self->win, attr_old);
-        return curses_window_check_err(self, rtn, "wattrset", "addnstr");
+        int attr_rtn = wattrset(self->win, attr_old);
+        if (rtn != ERR) {
+            rtn = attr_rtn;
+            funcname = "wattrset";
+        }
     }
-    Py_RETURN_NONE;
+    return curses_window_check_err(self, rtn, funcname, "addnstr");
 }
 
 /*[clinic input]
@@ -4094,15 +4092,14 @@ _curses_window_insstr_impl(PyCursesWindowObject *self, int group_left_1,
         }
         Py_DECREF(bytesobj);
     }
-    if (rtn == ERR) {
-        curses_window_set_error(self, funcname, "insstr");
-        return NULL;
-    }
     if (use_attr) {
-        rtn = wattrset(self->win, attr_old);
-        return curses_window_check_err(self, rtn, "wattrset", "insstr");
+        int attr_rtn = wattrset(self->win, attr_old);
+        if (rtn != ERR) {
+            rtn = attr_rtn;
+            funcname = "wattrset";
+        }
     }
-    Py_RETURN_NONE;
+    return curses_window_check_err(self, rtn, funcname, "insstr");
 }
 
 /*[clinic input]
@@ -4206,15 +4203,14 @@ _curses_window_insnstr_impl(PyCursesWindowObject *self, int group_left_1,
         }
         Py_DECREF(bytesobj);
     }
-    if (rtn == ERR) {
-        curses_window_set_error(self, funcname, "insnstr");
-        return NULL;
-    }
     if (use_attr) {
-        rtn = wattrset(self->win, attr_old);
-        return curses_window_check_err(self, rtn, "wattrset", "insnstr");
+        int attr_rtn = wattrset(self->win, attr_old);
+        if (rtn != ERR) {
+            rtn = attr_rtn;
+            funcname = "wattrset";
+        }
     }
-    Py_RETURN_NONE;
+    return curses_window_check_err(self, rtn, funcname, "insnstr");
 }
 
 /*[clinic input]

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