pi-oneline.py

print (lambda p:p[0]+'.'+p[1:])(
    str((lambda(x,y,t,a):2L*x*x//a)(
        (lambda F:(lambda S:reduce(
            lambda(x,y,t,a),_:((x+y)//2L,
                S((x*y)//F),2L*t,
                (a-(t*(((x+y)//2L)**2-
                       (S((x*y)//F))**2))//F)),
            [0]*13,(F,(F*F)//S(2L*F),2L,F//2L)))(
                lambda n:reduce(lambda x,_:(
                    x-x//2L+(n*F)//(2L*x)),
                [0]*15,
                n//2L)))(10L**(5010))))[:5000])