small challenge : fixpoint((x+1)**0.5 for x in itially(2))

[Azolex]

Paul McGuire wrote:
> Howzis?
> 
> -- Paul
> 
> 
> class Bag:
>     pass
> data = Bag()
> data.x = None
> 
> def itially(bar):
>     if data.x is None:
>         data.x = bar
>     while 1:
>         yield data.x
> 
> def limit(z):
>     eps = 1e-10
>     done = False
>     z2 = z.next()
>     z1 = z2 + 1
>     while abs(z2-z1) > eps:
>         data.x = z2
>         z2, z1 = z.next(),z2
>         print "dbg>",z1,z2
>     return z1
> 
> print limit( x**0.5 for x in itially(2) )

It fits the bill, I'd say. Below is my simplest solution, renaming 
"limit" to a more appropriate "fixpoint". Like yours, this solution as 
concurrency issues.

Note that (z+1)**0.5 has a more interesting attractive fixpoint that 
z**0.5, namely the golden mean 1.618...


def itially(z) :
     echoback.z = z
     while True :
         yield echoback.z

def echoback(gen) :
     while True :
         echoback.z = gen.next()
         yield echoback.z

def fixpoint(gen) :
     z = echoback(gen).next
     while True :
         if z()==z() :
             return z()

print fixpoint((z+1)**0.5 for z in itially(2))