Trace KeyboardInterrupt exception?

[andrewdalke at gmail.com]

Tony Nelson wrote:
> I'm trying to find out what is eating some KeyboardInterrupt exceptions
> in a fairly large program (yum).  My KeyboardInterrupt handler is called
> for some Ctl-C presses, but for others nothing seems to happen.

>  ... I'd like to use a debugger to trace
> KeyboardInterrupt exceptions, make sure that they're happening, and see
> what is handling them.

I don't know how to do that in Idle.  You can replace the default
Ctrl-C interrupt
handler with your own and use that to inspect the current stack.  For
example,

>>> import signal
>>> signal.getsignal(signal.SIGINT)
<built-in function default_int_handler>
>>> prev_handler = signal.getsignal(signal.SIGINT)
>>> def new_int_handler(*args):
...   print "Keyboard Interrupt!"
...   traceback.print_stack()
...   prev_handler(*args)
...
>>> signal.signal(signal.SIGINT, new_int_handler)
<built-in function default_int_handler>
>>> def spin():
...   while 1: pass
...
>>> import traceback
>>> spin()
^CKeyboard Interrupt!
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in spin
  File "<stdin>", line 3, in new_int_handler
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in spin
  File "<stdin>", line 4, in new_int_handler
KeyboardInterrupt
>>>

There's no real need to call the old handler.  You could "raise
KeyboardInterrupt"
or SystemExit or just ignore it, as in

>>> count = 0
>>> def new_int_handler(signum, frame):
...    global count
...    print messages[count]
...    if count >= len(messages)-1:
...       raise KeyboardInterrupt
...    count += 1
...
>>> messages = {0: "Sorry, did you want me to do something?",
...             1: "That's ticklish!",
...             2: "Now, where did that off button go to....",
...             3: "Do that again and I'll leave.",
...             4: "Shutdown activated"}
>>>
>>> def spin():
...   while 1: pass
...
>>> spin()
^CTraceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in spin
KeyboardInterrupt
>>>
>>> import signal
>>> signal.signal(signal.SIGINT, new_int_handler)
<built-in function default_int_handler>
>>>
>>> spin()
^CSorry, did you want me to do something?
^CThat's ticklish!
^CNow, where did that off button go to....
^CDo that again and I'll leave.
^CShutdown activated
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in spin
  File "<stdin>", line 5, in new_int_handler
KeyboardInterrupt
>>> 

                Andrew
                dalke at dalkescientific.com