python怎么调用pi

import sys

import math

defmain(argv):

    iflen(argv) !=1:

        sys.exit('Usage: calc_pi.py <n>')

    print'\nComputing Pi v.01\n'

    a=1.0

    b=1.0/math.sqrt(2)

    t=1.0/4.0

    p=1.0

    foriinrange(int(sys.argv[1])):

        at=(a+b)/2

        bt=math.sqrt(a*b)

        tt=t-p*(a-at)**2

        pt=2*p

        a=at;b=bt;t=tt;p=pt

    my_pi=(a+b)**2/(4*t)

    accuracy=100*(math.pi-my_pi)/my_pi

    print"Pi is approximately: "+str(my_pi)

    print"Accuracy with math.pi: "+str(accuracy)

if__name__=="__main__":

    main(sys.argv[1:])