From b589445fda69e9eacd94878a75ec09aa2fbf5ffd Mon Sep 17 00:00:00 2001
From: Vyron Vasileiadis <hi@fedonman.com>
Date: Mon, 17 Aug 2026 22:51:52 +0300
Subject: [PATCH] gh-155974: Restore the window attributes when a curses write
 fails

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.
---
 Lib/test/test_curses.py                       | 15 ++++++
 ...-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst |  4 ++
 Modules/_cursesmodule.c                       | 52 +++++++++----------
 3 files changed, 43 insertions(+), 28 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-08-17-22-51-22.gh-issue-155974.Qz3Vb7.rst

diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index f582336fae17344..6ab951ad2786ea8 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 000000000000000..8621bc49a03ccab
--- /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 006e27d55d8925d..0bab30184a357ad 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]