How on Factorial

Stefan Behnel stefan_ml at behnel.de
Thu Oct 28 19:48:14 CEST 2010


karmaguedon, 28.10.2010 18:46:
> On 27 oct, 10:27, Arnaud Delobelle wrote:
>> Chris Rebert writes:
>>> On Tue, Oct 26, 2010 at 11:25 PM, Geobird wrote:
>>
>>>>   I  am a beginner in Python and would ask for a help.
>>
>>>> I  was searching for  smaller  version  of  code  to calculate
>>>> factorial . Found  this one
>>>> def fact(x):
>>>>         return x>  1 and x * fact(x - 1) or 1
>>
>>>>   But I don't  really get how (  ....x>  1 and x * fact(x - 1)....)
>>>> works .
>>
>>> It exploits short-circuit evaluation
>>> (http://en.wikipedia.org/wiki/Short-circuit_evaluation). This is
>>> stunt coding / code golf; no one should actually write factorial like
>>> that.
>>
>> True.  It's far too verbose.  I'd go for something like:
>>
>>      f=lambda n:n<=0 or n*f(~-n)
>>
>> I've saved a few precious keystrokes and used the very handy ~- idiom!
>
> I didn't know the idiom, nice tip.

Not really. Given that many people won't know it, most readers will have a 
hard time deciphering the above code, so it's best not to do this.

Stefan




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