Demo/scripts/pi.py

   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 = 2, 4, 1, 12, 4
  15     while True:
  16         # Next approximation
  17         p, q, k = k*k, 2*k+1, k+1
  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 = 10*(a%b), 10*(a1%b1)
  24             d, d1 = a//b, a1//b1
  25
  26 def output(d):
  27     # Use write() to avoid spaces between the digits
  28     sys.stdout.write(str(d))
  29     # Flush so the output is seen immediately
  30     sys.stdout.flush()
  31
  32 if __name__ == "__main__":
  33     main()