[Tutor] Newbie Question on Exceptions...

[Andre Engels]

2007/5/8, dsh0105 at comcast.net <dsh0105 at comcast.net>:
> I'm working my way through the book "beginning python" and I came across an exercise that suggests using Exception trapping to see if a value is in a dictionary:
>
> fridge={"apple":"A shiny red apple","pear":"a nice ripe pear","grapes":"seadless grapes"}
> food_sought="apple"
> fridge_list=fridge.keys();
> try:
>     print "The fridge contains %s" %fridge[food_sought]
> except (KeyError):
>     print "The fridge does not contain %s"%food_sought
>
> I'm fairly certain the book is in error in calling this a "short-cut" since the has_key method is much less verbose to use,

Is it?

if fridge.has_key(food_sought):
    foo
else:
    bar

doesn't look much less verbose than:

try:
    foo
except (KeyError):
    bar

> but it brings up a question about exceptions in general:
>
> In Java using exceptions in the way shown above is a classic anti-pattern since Exceptions should only be used for..well exceptional conditions.
>
> Is the same true of Python? Or is ok to use Exception handling like the book suggests?

Exceptions are in general much more freely used in Python than in most
other languages, it's called the "EAFP" (It's easier to ask
forgiveness than to get permission) style, instead of the "LBYL" (look
before you leap) style most other languages use.


-- 
Andre Engels, andreengels at gmail.com
ICQ: 6260644  --  Skype: a_engels