Question about exception-handling mechanism

[Gordon McMillan]

willfg at my-deja.com wrote


> ...A colleague asked why in an exception handling mechanism
> you'd want the ELSE block to be executed if you don't throw an
> exception as opposed to a FINALLY block. Anyone used this feature
> in practice? Thanks in advance for your input, -- Will

A finally clause is *always* executed, so it's not really in 
competition with a try / else. If everything goes fine, these are 
equivalent:

try:
  do_something()
  do_morestuff()
except NoBananasException:
  yesweaint()

try:
  do_something()
except NoBananasException:
  yesweaint()
else:
  do_morestuff()

Now we expect do_something() to sometimes throw a specific 
exception, and we're prepared to deal with it. But we can't deal 
with the same exception coming from do_morestuff(). So the 
first snippet may cause a problem by "recovering" from the 
wrong error. That's the rationale for try / else, (essentially, we 
don't have to use a flag variable).

- Gordon