import math

def average(values):
	"Compute the average and standard deviation of a list of numbers"
	sum = 0.0		# Note that we start with floating point number
	squaredSum = 0.0
	for v in values:
		sum += v
		squaredSum += v * v
	avg = sum / len(values)
	squaredAvg = squaredSum / len(values)
	variance = squaredAvg - avg * avg
	stdDev = math.sqrt(variance)
	return avg, stdDev

class Data:
	"Computes statistics for a list of values."

	def __init__(self, values=[]):
		"Initialize accumulators and add in initial values."
		self.sum = 0.0
		self.squaredSum = 0.0
		self.count = 0
		for v in values:
			self.addValue(v)

	def addValue(self, v):
		self.sum += v
		self.squaredSum += v * v
		self.count += 1

	def average(self):
		return self.sum / self.count

	def variance(self):
		avg = self.average()
		return self.squaredSum / self.count - avg * avg

	def standardDeviation(self):
		return math.sqrt(self.variance())

if __name__ == "__main__":
	values = [4, 9, 11, 12, 17, 5, 8, 12, 14]
	print average(values)
	s = Data(values)
	print s.average(), s.variance(), s.standardDeviation()
	#print average([1.0, 2.0, 3.0, 2.0, 1.0])
	#print average([1.0, 20.0, 30.0, 1.0, 1.0])