gh-151744: Add curses.nofilter() (GH-151747)

Wrap the ncurses nofilter() function, which undoes the effect of
filter().  Without it there is no way to restore normal screen sizing
after a curses.filter() call in the same process.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Doc/library/curses.rst

@@ -204,6 +204,17 @@ The module :mod:`!curses` defines the following functions:
    character-at-a-time  line editing without touching the rest of the screen.
 
 
+.. function:: nofilter()
+
+   Undo the effect of a previous :func:`.filter` call.
+   Like :func:`.filter`, it must be called before :func:`initscr` so that the
+   next initialization uses the full screen again.
+
+   Availability: if the underlying curses library provides ``nofilter()``.
+
+   .. versionadded:: next
+
+
 .. function:: flash()
 
    Flash the screen.  That is, change it to reverse-video and then change it back

Doc/whatsnew/3.16.rst

@@ -86,6 +86,12 @@ New modules
 Improved modules
 ================
 
+curses
+------
+
+* Add :func:`curses.nofilter`, which undoes the effect of :func:`curses.filter`.
+  (Contributed by Serhiy Storchaka in :gh:`151744`.)
+
 gzip
 ----
 

Lib/test/test_curses.py

@@ -120,8 +120,9 @@ def setUp(self):
     @requires_curses_func('filter')
     def test_filter(self):
         # TODO: Should be called before initscr() or newterm() are called.
-        # TODO: nofilter()
         curses.filter()
+        if hasattr(curses, 'nofilter'):
+            curses.nofilter()
 
     @requires_curses_func('use_env')
     def test_use_env(self):

Misc/NEWS.d/next/Library/2026-06-19-18-40-00.gh-issue-151744.Kp7mNq.rst

@@ -0,0 +1 @@
+Add :func:`curses.nofilter`, which undoes the effect of :func:`curses.filter`.

Modules/_cursesmodule.c

@@ -3220,6 +3220,28 @@ _curses_filter_impl(PyObject *module)
 }
 #endif
 
+#ifdef HAVE_CURSES_NOFILTER
+/*[clinic input]
+_curses.nofilter
+
+Undo the effect of a preceding filter() call.
+
+Must be called before initscr().  It restores the normal behaviour
+disabled by filter(), so that the next initscr() uses the full screen
+rather than a single line.
+[clinic start generated code]*/
+
+static PyObject *
+_curses_nofilter_impl(PyObject *module)
+/*[clinic end generated code: output=d95ca4d48a6bdbdf input=58aea83b1a5c969f]*/
+{
+    /* not checking for PyCursesInitialised here since nofilter() must
+       be called before initscr() */
+    nofilter();
+    Py_RETURN_NONE;
+}
+#endif
+
 /*[clinic input]
 _curses.baudrate
 
@@ -5321,6 +5343,7 @@ static PyMethodDef cursesmodule_methods[] = {
     _CURSES_ENDWIN_METHODDEF
     _CURSES_ERASECHAR_METHODDEF
     _CURSES_FILTER_METHODDEF
+    _CURSES_NOFILTER_METHODDEF
     _CURSES_FLASH_METHODDEF
     _CURSES_FLUSHINP_METHODDEF
     _CURSES_GETMOUSE_METHODDEF

Modules/clinic/_cursesmodule.c.h

@@ -7192,6 +7192,7 @@ PY_CHECK_CURSES_FUNC([immedok])
 PY_CHECK_CURSES_FUNC([syncok])
 PY_CHECK_CURSES_FUNC([wchgat])
 PY_CHECK_CURSES_FUNC([filter])
+PY_CHECK_CURSES_FUNC([nofilter])
 PY_CHECK_CURSES_FUNC([has_key])
 PY_CHECK_CURSES_FUNC([typeahead])
 PY_CHECK_CURSES_FUNC([use_env])

configure

@@ -218,6 +218,9 @@
 /* Define if you have the 'is_term_resized' function. */
 #undef HAVE_CURSES_IS_TERM_RESIZED
 
+/* Define if you have the 'nofilter' function. */
+#undef HAVE_CURSES_NOFILTER
+
 /* Define if you have the 'resizeterm' function. */
 #undef HAVE_CURSES_RESIZETERM