Fun and games with lambda

[Steven D'Aprano]

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

[Wolfgang Rohdewald]

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

[Ian Kelly]

On Fri, Jun 17, 2011 at 10:56 AM, Wolfgang Rohdewald
<wolf...@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.

[Mark Dickinson]

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

[Chris Angelico]

On Sat, Jun 18, 2011 at 2:10 AM, Steven D'Aprano
<steve+comp....@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