cpython/Demo/scripts/pi.py

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#! /usr/local/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
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while 1:
# Next approximation
p, q, k = k*k, 2L*k+1L, k+1L
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a, b, a1, b1 = a1, b1, p*a+q*a1, p*b+q*b1
# Print common digits
d, d1 = a/b, a1/b1
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while d == d1:
output(d)
a, a1 = 10L*(a%b), 10L*(a1%b1)
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d, d1 = a/b, a1/b1
def output(d):
# Use write() to avoid spaces between the digits
# Use int(d) to avoid a trailing L after each digit
sys.stdout.write(`int(d)`)
# Flush so the output is seen immediately
sys.stdout.flush()
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main()