[Tutor] How to exit this loop in the interpreter

[Jerry Hill]

On Thu, May 3, 2012 at 9:57 AM,  <spawgi at gmail.com> wrote:
> Hello all,
>
> I have encountered the following scenario.
> Here is the code - on IDLE on Windows XP.
>
>>>> while True:
>     try:
>         number = raw_input("enter number - ")
>         print number * number
>     except ValueError:
>         print "invalid number"
>     except:
>         print "unspecified exception"
>     else:
>         print "other conditions"
>
>
> enter number - 3
> unspecified exception
>
> What I noticed is that no matter, what input I give, I cannot exit this
> loop. I have tried control-C, control-D etc. all the keys. So how can I exit
> from this loop?

You can't, because you've painted yourself into a corner.  The bare
"except:" line will catch any exception at all.  Including the
KeyboardInterrupt exception that is raised when you hit control-c.  If
you must catch unknown exceptions, but still want to allow the
KeyboardInterrupt exception from pressing control-c to exit your
program, then use "except Exception:"
 instead of a bare "except:" statement.  Since KeyboardInterrupt (and
SystemExit) are not subclasses of Exception, they won't be caught.

KeyboardInterrupt and SystemExit are subclasses of a class called
BaseException, instead of Exception, for this exact purpose.  See more
about python's exception hierarchy here:
http://docs.python.org/library/exceptions.html

-- 
Jerry