standard_deviation.py

from __future__ import division
from math import sqrt, pow

class StandardDeviation(object):
    
	def do_round(self, data):
		data = "%.3f" % round(data, 3)
		return float(data)
	
	def do_diff(self, n, mean):
		return pow((n-mean), 2)
			
	def standDev(self, data_list):
	    mean = sum(data_list)/len(data_list)
	    result = sqrt(sum([self.do_diff(s, mean) for s in \
	data_list] )/len(data_list))
	    return float(self.do_round(result))

if __name__=='__main__':
	data_list = [2, 4, 4, 4, 5, 5, 7, 9 ]
	std = StandardDeviation()
	print std.standDev(data_list)