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Fun and games with lambda

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  Fun and games with lambda Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-17 16:10 +0000
    Re: Fun and games with lambda Wolfgang Rohdewald <wolfgang@rohdewald.de> - 2011-06-17 18:56 +0200
    Re: Fun and games with lambda Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-17 11:07 -0600
    Re: Fun and games with lambda Mark Dickinson <mdickinson@enthought.com> - 2011-06-17 12:02 -0700
    Re: Fun and games with lambda Chris Angelico <rosuav@gmail.com> - 2011-06-18 10:40 +1000

#7830 — Fun and games with lambda

If you've ever wondered what lambda and reduce are good for, run this one-
liner and wonder no more...

(Be patient, it may take a few seconds to return.)

# Python 2 version:

print((lambda f:((lambda p:p[0]+'.'+p[1:])(str((lambda Q:2*Q[0]*Q[0]//Q
[3])((lambda F:(lambda S:f(lambda T,_:((T[0]+T[1])//2,S((T[0]*T[1])//
F),2*T[2],(T[3]-(T[2]*(((T[0]+T[1])//2)**2-(S((T[0]*T[1])//F))**2))//F)),
[0]*13,(F,(F*F)//S(2*F),2,F//2)))(lambda n:f(lambda x,_:(x-x//2+(n*F)//
(2*x)),[0]*15,n//2)))(10**(5010))))[:5000])))(reduce))

# Python 3 version:

print((lambda f:((lambda p:p[0]+'.'+p[1:])(str((lambda Q:2*Q[0]*Q[0]//Q
[3])((lambda F:(lambda S:f(lambda T,_:((T[0]+T[1])//2,S((T[0]*T[1])//
F),2*T[2],(T[3]-(T[2]*(((T[0]+T[1])//2)**2-(S((T[0]*T[1])//F))**2))//F)),
[0]*13,(F,(F*F)//S(2*F),2,F//2)))(lambda n:f(lambda x,_:(x-x//2+(n*F)//
(2*x)),[0]*15,n//2)))(10**(5010))))[:5000])))(__import__
('functools').reduce))


I can't take credit for this little beauty. It originally came from 
Manuel Garcia, all I did was make it compatible with Python 3 and add 
some additional, but trivial, obfuscation.

See the original post here:
http://web.archiveorange.com/archive/v/5H3d1yQN5N15HEgOWHMx



Encouraging-hatred-of-lambdas-for-fun-and-profit-ly y'rs,


-- 
Steven

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#7833

On Freitag 17 Juni 2011, Steven D'Aprano wrote:
> run this one-
> liner and wonder no more...

looks like something dangerous to me. What does
it do? rm -rf ?

-- 
Wolfgang

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#7837

On Fri, Jun 17, 2011 at 10:56 AM, Wolfgang Rohdewald
<wolfgang@rohdewald.de> wrote:
> On Freitag 17 Juni 2011, Steven D'Aprano wrote:
>> run this one-
>> liner and wonder no more...
>
> looks like something dangerous to me. What does
> it do? rm -rf ?

The thread at the link discusses what it does in great detail.

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#7845

On Jun 17, 5:10 pm, Steven D'Aprano <steve
+comp.lang.pyt...@pearwood.info> wrote:
>
> print((lambda f:((lambda p:p[0]+'.'+p[1:])(str((lambda Q:2*Q[0]*Q[0]//Q
> [3])((lambda F:(lambda S:f(lambda T,_:((T[0]+T[1])//2,S((T[0]*T[1])//
> F),2*T[2],(T[3]-(T[2]*(((T[0]+T[1])//2)**2-(S((T[0]*T[1])//F))**2))//F)),
> [0]*13,(F,(F*F)//S(2*F),2,F//2)))(lambda n:f(lambda x,_:(x-x//2+(n*F)//
> (2*x)),[0]*15,n//2)))(10**(5010))))[:5000])))(reduce))

Very nice, but a little unnatural.  Can't you find room to stick an
extra factor of 2 in there somewhere?

(See also: http://bugs.python.org/issue12345 )

--
Mark

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#7872

On Sat, Jun 18, 2011 at 2:10 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> If you've ever wondered what lambda and reduce are good for, run this one-
> liner and wonder no more...
>
> (Be patient, it may take a few seconds to return.)

I have a decent CPU so it's not too bad. And the precision produced is
noteworthy. However, I have no idea how it does its work, so I'm just
in awe of the quality of the code.

And you can read that last remark either way.

ChrisA

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