[3.13] gh-157672: Keep Python's signal handlers when Tk is initialized on macOS (GH-157673) (GH-157989)

Tk on macOS replaces the SIGINT, SIGHUP and SIGTERM handlers with its
own, which exits the process, so Ctrl-C terminated a tkinter program
instead of raising KeyboardInterrupt.  Save the handlers installed by
Python before Tk_Init() and restore them after it.

This affects Tk 8.6.11 to 8.6.18 and 9.0 to 9.0.4.  Tk itself is fixed
in 8.6.19 and 9.0.5.

(cherry picked from commit 4532b36)

On 3.13 there was no Tkinter_TkInit(), and tkappinit.c, which is used
when Python is built with WITH_APPINIT (as on macOS), called Tk_Init()
directly, bypassing the fix.

Author: serhiy-storchaka

Lib/test/test_tkinter/test_misc.py

@@ -1,5 +1,6 @@
 import functools
 import platform
+import signal
 import sys
 import textwrap
 import unittest
@@ -9,6 +10,7 @@
 import enum
 from test import support
 from test.support import os_helper
+from test.support.isolation import runInSubprocess
 from test.support.script_helper import assert_python_ok
 from test.test_tkinter.support import setUpModule  # noqa: F401
 from test.test_tkinter.support import (AbstractTkTest, AbstractDefaultRootTest,
@@ -1901,5 +1903,17 @@ def _info_commands(widget, pattern=None):
     return widget.tk.splitlist(widget.tk.call('info', 'commands', pattern))
 
 
+class SignalTest(unittest.TestCase):
+
+    @runInSubprocess()
+    def test_sigint_handler(self):
+        # gh-157672: Tk on macOS replaced the SIGINT handler with its own,
+        # which exits the process.
+        root = tkinter.Tk()
+        self.addCleanup(root.destroy)
+        with self.assertRaises(KeyboardInterrupt):
+            signal.raise_signal(signal.SIGINT)
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2026-09-17-14-00-00.gh-issue-157672.tksigs.rst

@@ -0,0 +1,4 @@
+Fix :mod:`tkinter` on macOS: creating a :class:`~tkinter.Tk` instance no
+longer replaces the Python handlers of SIGINT, SIGHUP and SIGTERM with Tk's
+handler which exits the process, so Ctrl-C raises :exc:`KeyboardInterrupt`
+again.

Modules/_tkinter.c

@@ -33,6 +33,8 @@ Copyright (C) 1994 Steen Lumholt.
 #include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_sysmodule.h"     // _PySys_GetOptionalAttrString()
 
+#include <signal.h>               // SIGINT
+
 #ifdef MS_WINDOWS
 #  include <windows.h>
 #endif
@@ -538,6 +540,30 @@ class _tkinter.tktimertoken "TkttObject *" "&Tktt_Type_spec"
 int Tcl_AppInit(Tcl_Interp *);
 #endif
 
+int
+Tkinter_TkInit(Tcl_Interp *interp)
+{
+#ifdef __APPLE__
+    /* Tk on macOS replaces the handlers of these signals with its own,
+       which exits the process.  Keep the handlers installed by Python
+       (gh-157672). */
+    static const int signals[] = {SIGINT, SIGHUP, SIGTERM};
+    PyOS_sighandler_t handlers[Py_ARRAY_LENGTH(signals)];
+    for (size_t i = 0; i < Py_ARRAY_LENGTH(signals); i++) {
+        handlers[i] = PyOS_getsig(signals[i]);
+    }
+#endif
+    int result = Tk_Init(interp);
+#ifdef __APPLE__
+    for (size_t i = 0; i < Py_ARRAY_LENGTH(signals); i++) {
+        if (handlers[i] != SIG_DFL) {
+            PyOS_setsig(signals[i], handlers[i]);
+        }
+    }
+#endif
+    return result;
+}
+
 #ifndef WITH_APPINIT
 int
 Tcl_AppInit(Tcl_Interp *interp)
@@ -556,7 +582,7 @@ Tcl_AppInit(Tcl_Interp *interp)
         return TCL_OK;
     }
 
-    if (Tk_Init(interp) == TCL_ERROR) {
+    if (Tkinter_TkInit(interp) == TCL_ERROR) {
         PySys_WriteStderr("Tk_Init error: %s\n", Tcl_GetStringResult(interp));
         return TCL_ERROR;
     }
@@ -2980,7 +3006,7 @@ _tkinter_tkapp_loadtk_impl(TkappObject *self)
         return NULL;
     }
     if (_tk_exists == NULL || strcmp(_tk_exists, "1") != 0)     {
-        if (Tk_Init(interp)             == TCL_ERROR) {
+        if (Tkinter_TkInit(interp)      == TCL_ERROR) {
             Tkinter_Error(self);
             return NULL;
         }

Modules/tkappinit.c

@@ -37,7 +37,7 @@ Tcl_AppInit(Tcl_Interp *interp)
         return TCL_OK;
     }
 
-    if (Tk_Init(interp) == TCL_ERROR) {
+    if (Tkinter_TkInit(interp) == TCL_ERROR) {
         return TCL_ERROR;
     }
 

Modules/tkinter.h

@@ -16,4 +16,6 @@
                         (TK_RELEASE_LEVEL << 8) | \
                         (TK_RELEASE_SERIAL << 0))
 
+int Tkinter_TkInit(Tcl_Interp *interp);
+
 #endif /* !TKINTER_H */