tkinter: Tk on macOS replaces Python's SIGINT, SIGHUP and SIGTERM handlers, so Ctrl-C exits instead of raising KeyboardInterrupt

Bug report

Since Tk 8.6.11, TkpInit() on macOS installs its own C-level handler for SIGINT, SIGHUP and SIGTERM, which calls Tcl_Exit(1) (tkMacOSXInit.c, Tk ticket f3e96942ed). It does this unconditionally, so Python's handler is replaced as soon as a Tk instance is created. signal.getsignal() still returns the Python handler, but it is never called.

import signal, time, tkinter
print(signal.getsignal(signal.SIGINT))  # <built-in function default_int_handler>
root = tkinter.Tk()
time.sleep(60)  # press Ctrl-C

On macOS the process exits silently with status 1 instead of raising KeyboardInterrupt. Python-level handlers set with signal.signal() for SIGTERM and SIGHUP are disabled the same way.

This also affects IDLE: with #157662, which interrupts user code with a real SIGINT, Ctrl-C in the Shell would terminate the user process on macOS once the user's code has created a Tk window. On the macOS CI the test_idle worker exits with status 1 for the same reason, since GUI tests earlier in the same process created Tk windows.

The fix on the Tk side is on branch mac-signal-handlers, but installed Tk builds will not have it for a long time. _tkinter should save the handlers of these signals before Tk_Init() and restore them after it.

Linked PRs

• gh-157673

Comienza en _tkinter, en la llamada a Tk_Init(), y rastrea cómo se ven afectados los manejadores de señales de macOS. Reproduce el problema con el script de tkinter proporcionado y, después, verifica que crear una instancia de Tk conserve los manejadores de Python y que Ctrl-C genere una KeyboardInterrupt.