if or exception

Christopher T King squirrel at WPI.EDU
Thu Jul 29 15:17:00 CEST 2004


On Thu, 29 Jul 2004, Thomas Lindgaard wrote:

> Just wondering what is "the right thing to do":
> 
> number = 0
> if len(list) > 0: number = anotherNumber / len(list)
> 
> or 
> 
> try:
>   number = anotherNumber / len(list)
> except:
>   number = 0

The first will be faster if you expect len(list) to be zero very often, 
whereas the latter will be faster if you expect it to be zero very rarely.

This is because in the normal case, the latter needs no extra code (except 
a quick 'setup try block'), whereas the former requires a function call 
and a comparison for all cases.  In the exceptional case, the latter must 
raise an catch an exception, which (I believe) is more expensive than the 
check in the former.  How much more expensive, I'm not qualified to say ;)




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