[Tutor] Please critique my Fraq.py (original) (raw)

Alan Gauld alan.gauld at blueyonder.co.uk
Sun Jul 25 13:59:26 CEST 2004

In Frac.py I wanted to give the user a chance to quit at any prompt (and have the program close smoothly), by entering a "q" or an "x". I did this by the statement,

if answer in ["q", "x"]: break

if answer in "qxQX": break

is probably neater - to my eyes anyway, certainly less storage although thats not likely to be an issue! :-)

The problem with this is that it only breaks out of the inner loop. I have to repeat this statement in the outer loop.

So I'm asking if there's a better way. Raising an exception doesn't do it.

Why does raising SystemExit not do it? In particular if you move all cleanup code - closing files etc into a try/finally block the exception route is the preferred method.

Is there a way (other than mine) to enable the user to quit smoothly when he's inside a loop which is inside a loop?

Nope, an exception is the only reliable way to jump out of nested loops. It could be SystemExit to quit the program or it could be a user defined one

class LoopExit(exception): pass

try: while True: while True: try: raise LoopBreak finally: print "Done!" except LoopBreak: print "I escaped!"

HTH

Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld

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