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
30dde1e 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.

Author: fedonman

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.

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.

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]