gistfile1.pyw

#!/usr/bin/env python
#
# Simulates a leveraged ETF, with a stop-loss ability. The default model assumes
# that you guess right 1/3 times, and when you guess right the ETF increases in
# value by 4% and when you guess wrong the ETF decreases in value by 2%.

import optparse
import random

def main(opts):
	capital = opts.principal
	for x in xrange(opts.runs):
		if random.random() < 1.0 / opts.accuracy:
			change = capital * opts.volatility / 100.0
			capital += change
			msg = '+$%1.2f' % (change,)
		else:
			change = capital * opts.stop_volatility / 100.0
			capital -= change
			msg = '-$%1.2f' % (change,)
		msg += ' ' * (10 - len(msg))
		msg += '$%1.2f' % (capital,)
		print msg
	print 'final: $%1.2f' % capital

if __name__ == '__main__':
	parser = optparse.OptionParser()
	parser.add_option('--accuracy', dest='accuracy', type='float', default=3.0,
					  help='1/N times you guess right; default N = 3')
	parser.add_option('--principal', dest='principal', type='float', default=1000.0,
					  help='how much capital you start with')
	parser.add_option('--volatility', dest='volatility', type='float', default=4.0,
					  help='the percentage increase when you guess right; default is 4%')
	parser.add_option('--stop-volatility', dest='stop_volatility', type='float', default=2.0,
					  help='if you guess wrong, you lose this amount; default is 2%')
	parser.add_option('--runs', dest='runs', type='int', default=100,
					  help='how many days to simulate')
	opts, args = parser.parse_args()
	main(opts)