cpython/Demo/scripts/pi.py

#! /usr/bin/env python

# Print digits of pi forever.
#
# The algorithm, using Python's 'long' integers ("bignums"), works
# with continued fractions, and was conceived by Lambert Meertens.
#
# See also the ABC Programmer's Handbook, by Geurts, Meertens & Pemberton,
# published by Prentice-Hall (UK) Ltd., 1990.

import sys

def main():
    k, a, b, a1, b1 = 2L, 4L, 1L, 12L, 4L
    while 1:
        # Next approximation
        p, q, k = k*k, 2L*k+1L, k+1L
        a, b, a1, b1 = a1, b1, p*a+q*a1, p*b+q*b1
        # Print common digits
        d, d1 = a/b, a1/b1
        while d == d1:
            output(d)
            a, a1 = 10L*(a%b), 10L*(a1%b1)
            d, d1 = a/b, a1/b1

def output(d):
    # Use write() to avoid spaces between the digits
    # Use str() to avoid the 'L'
    sys.stdout.write(str(d))
    # Flush so the output is seen immediately
    sys.stdout.flush()

main()