[Pyfltk-user] Quitting a pyfltk application with Ctrl-c

[Dima K. <di...@se...>]

Hello.

This is another issue i just looked into, that I would appreciate some
pointers for. I have this trivial pyfltk program:

  #!/usr/bin/python3

  from fltk import *

  window = Fl_Window(100,200,"xxx")
  window.end()
  window.show()

  Fl.run()

I run it. Instead of hitting Escape, I go back to the console, and hit
Ctrl-c. I expect the program to exit, but it ignores the C-c, and does
nothing. If I go back to the application, and hit Escape, it does exit,
but also says this:

  Traceback (most recent call last):
    File "/home/dima/projects/mrcam/tst.py", line 9, in <module>
      Fl.run()
      ~~~~~~^^
    File "/usr/lib/python3/dist-packages/fltk/fltk.py", line 3292, in run
      return _fltk.Fl_run(*args)
             ~~~~~~~~~~~~^^^^^^^
  KeyboardInterrupt

I vaguely remember seeing this in other contexts before. This was years
ago, but back then, when Python called an extension-module function it
reset the SIGINT handler to a function that sets a flag, and does
nothing else. Then when the extension module function returned, it would
look at the flag, and respond to it at that time. This would cause us to
ignore C-c until the Python interpreter got control back. I actually
work around this in all my extension modules. For instance:

  https://github.com/dkogan/mrcam/blob/f37ea3577567e4bd64fe3b69a8196c48f538ee03/mrcam-pywrap.c#L30

At the top of any extension-module function that is not expected to
return immediately, I SET_SIGINT(), and RESET_SIGINT() when done. Do we
need to do something vaguely similar here? pyfltk should allow the
expected thing to happen: when we get a Ctrl-c, the application should
exit.

As with the previous email, this is on a very recent Debian system with:

  $ dpkg -l python3-fltk libfltk1.4 python3
  ii  python3-fltk:amd64 1.4.2.0-2    amd64  Python wrapper for the Fast Light Toolkit
  ii  libfltk1.4:amd64   1.4.3-1      amd64  Fast Light Toolkit - main shared library
  ii  python3            3.13.1-2     amd64  interactive high-level object-oriented language (default python3 version)

Thanks