Python pi calculation?

Question

I am a python beginner and I want to calculate pi. I tried using the Chudnovsky algorithm because I heard that it is faster than other algorithms.

This is my code:

Answer 1

from decimal import *

#Sets decimal to 25 digits of precision
getcontext().prec = 25

def factorial(n):
    if n<1:
        return 1
    else:
        return n * factorial(n-1)

def plouffBig(n): #http://en.wikipedia.org/wiki/Bailey%E2%80%93Borwein%E2%80%93Plouffe_formula
    pi = Decimal(0)
    k = 0
    while k < n:
        pi += (Decimal(1)/(16**k))*((Decimal(4)/(8*k+1))-(Decimal(2)/(8*k+4))-(Decimal(1)/(8*k+5))-(Decimal(1)/(8*k+6)))
        k += 1
    return pi

def bellardBig(n): #http://en.wikipedia.org/wiki/Bellard%27s_formula
    pi = Decimal(0)
    k = 0
    while k < n:
        pi += (Decimal(-1)**k/(1024**k))*( Decimal(256)/(10*k+1) + Decimal(1)/(10*k+9) - Decimal(64)/(10*k+3) - Decimal(32)/(4*k+1) - Decimal(4)/(10*k+5) - Decimal(4)/(10*k+7) -Decimal(1)/(4*k+3))
        k += 1
    pi = pi * 1/(2**6)
    return pi

def chudnovskyBig(n): #http://en.wikipedia.org/wiki/Chudnovsky_algorithm
    pi = Decimal(0)
    k = 0
    while k < n:
        pi += (Decimal(-1)**k)*(Decimal(factorial(6*k))/((factorial(k)**3)*(factorial(3*k)))* (13591409+545140134*k)/(640320**(3*k)))
        k += 1
    pi = pi * Decimal(10005).sqrt()/4270934400
    pi = pi**(-1)
    return pi
print "\t\t\t Plouff \t\t Bellard \t\t\t Chudnovsky"
for i in xrange(1,20):
    print "Iteration number ",i, " ", plouffBig(i), " " , bellardBig(i)," ", chudnovskyBig(i)