Calculating factorial

[Roger Hansen]

* Raymond Hettinger
>
> Olli Rajala wrote:
> 
> > Hi!
> > I've learned a few time Python and programming.  I wrote a function
> > that calculates a factorial of N and I was wondering if it's the best
> > (I think it's not. =) way to do that. I'm glad to hear your comments.
> >
> > def factorial(f):
> >     result = 1
> >     for number in range(1, f + 1):
> >         result = result * number
> >     return result
> >
> > print factorial(10)
> 
> I like your version just fine.  It's simple, clear, and it work's.
> Do consider changing line 2 to:  result = 1L so you can
> handle fact(50).

Agree! it's a nice version. But I think the recursive version is even
clearer. 

>>> def fact(n):
...     if n > 1:
...         return n*fact(n-1)
...     return 1
... 
>>> fact(4)
24

You can change line 3 with 
...         return long(n)*fact(n-1)

and you have long integers

>>> fact(50)
30414093201713378043612608166064768844377641568960512000000000000L


> If you want to make something hard out of something simple, try:
>  def fact(n): return reduce( lambda x,y:x*y, range(2,n+1), 1L )

:-)


R