[Tutor] Callbacks and exception handling

[Alan Gauld]

"Pete" <pkoek11 at xs4all.nl> wrote

> One thing though - I noticed that when an exception is raised in the
> callback function, that exception doesn't actually "show up" in the
> calling program.

Yes it does and Steven has answered that so maybe you are clear now.

But just to clarify, when you set a callback there is no guarantee 
that
the callback gets used immediately so the exception will not 
necessarily
appear in the setting function, it will appear in the calling 
function.


cb = []

def setcb(f):
    cb.append(f)

def fireworks():
    try:
       for f in cb: print f()    # call them all now
   except:
        print 'a callback failed'

def myFunc()
     setcb('lambda : len(cb))
     setcb('lambda : 42)
     setcb('lambda : 66)
     setcb('lambda : 12/0)   #oops!

myFunc()
fireworks()

Here any exceptions in the callback functions won't appear until
the fireworks function, they will not show up in myFunc.

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/