Chudnovsky

from math import*
from decimal import*
f,D=factorial,Decimal
pi=lambda i:exec("getcontext().prec+=i*9")or 1/(sum((D(-1+k%2*2)*D(f(k*6))*(k*545140134+13591409))/(D(f(k*3))*D(f(k))**3*D("640320")**(k*3+1.5))for k in range(i))*-12)