leibniz.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys

if len(sys.argv) < 2:
	sys.exit('Usage: %s [INTEGER]' % sys.argv[0])

try:
	n = int( sys.argv[1] )
except ValueError:
	sys.exit('Usage: %s [INTEGER]' % sys.argv[0])

sum = 0

for i in range(n):
	delta = 4.0 / (2*i +1)
	if   i % 2 == 0:
		sum += delta
	elif i % 2 == 1:
		sum -= delta
	else:
		print('only non-negitive integers')


print( "\nLeibniz approximation for π after " + str(n) + " iterations:\n\n" 
		+ str(sum) + "\n" )