1 #! /usr/bin/env python

     2 

     3 # Print digits of pi forever.

     4 #

     5 # The algorithm, using Python's 'long' integers ("bignums"), works

     6 # with continued fractions, and was conceived by Lambert Meertens.

     7 #

     8 # See also the ABC Programmer's Handbook, by Geurts, Meertens & Pemberton,

     9 # published by Prentice-Hall (UK) Ltd., 1990.

    10 

    11 import sys

    12 

    13 def main():

    14     k, a, b, a1, b1 = 2L, 4L, 1L, 12L, 4L

    15     while 1:

    16         # Next approximation

    17         p, q, k = k*k, 2L*k+1L, k+1L

    18         a, b, a1, b1 = a1, b1, p*a+q*a1, p*b+q*b1

    19         # Print common digits

    20         d, d1 = a//b, a1//b1

    21         while d == d1:

    22             output(d)

    23             a, a1 = 10L*(a%b), 10L*(a1%b1)

    24             d, d1 = a//b, a1//b1

    25 

    26 def output(d):

    27     # Use write() to avoid spaces between the digits

    28     # Use str() to avoid the 'L'

    29     sys.stdout.write(str(d))

    30     # Flush so the output is seen immediately

    31     sys.stdout.flush()

    32 

    33 if __name__ == "__main__":

    34     main()