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 = 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 int(d) to avoid a trailing L after each digit
  29         sys.stdout.write(`int(d)`)
  30         # Flush so the output is seen immediately
  31         sys.stdout.flush()
  32
  33 main()