MRAB writes:
How about 2 (or 3?) in rapid succession ("here's a CTRL-C, and here's another one to show I mean it!" :-)).
That's more complexity than you want to put in a signal handler. The way Emacs handles this is that the signal handler just enqueues a quit event, and the event loop checks for it and handles it. In other places (such as looping functions) more complex QUIT processing (that checks for repeated signals and throws to the innermost QUIT catcher) is done, but this can only be done in "safe" places, not in the signal handler itself. I imagine Python works the same way and it works fine in pure Python programs, too. The problem here is that when you return from the signal handler, you're trapped inside a poorly-written (for this purpose) C extension, and Python never gets to check for the first quit, let alone repeated ones. In Emacs it's pretty rare to get those, because Emacs is quite hostile to third-party C extensions, so C code QUIT-ified by the maintainers before it's allowed to be added. Python has lots of C extensions, and some are going to need QUIT occasionally -- but not often enough for the extension maintainer to notice and handle it. :-P