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2.1, 3.3, 4.5, 2.6, 3.7, 4.8

#!/usr/bin/env python3.5

from math import sqrt

class Calc_Mean_SD(object):

    def parse_comma_file(self, file):
        '''Parse comma separated float numbers.'''
        float_nums = []
        for line in file:
            substrs = line.split(',', line.count(','))
            for str_var in substrs:
                float_nums.append(float(str_var))
        return float_nums

    def calc_mean(self, numbers):
        '''Calculate mean from list of numbers. Iterate through list. 
        Add each number to sum. Calculate mean. Return mean value.'''
        sum = 0.0
        for number in numbers:
            sum += number
        mean = sum / len(numbers)
        return mean

    def calc_sd(self, numbers, mean):
        '''Calculate standard deviation. Iterate through list.
        Calculate single deviation, and add to single_dev.'''
        deviation = 0.0
        single_dev = 0.0
        for number in numbers:
            single_dev = number - mean
            deviation += (single_dev ** 2)
        standard_deviation = sqrt(deviation / (len(numbers) -1))
        return standard_deviation

    def run(self, filename):
        in_file = open(filename, 'r')
        numbers = self.parse_comma_file(in_file)
        mean = self.calc_mean(numbers)
        standard_deviation = self.calc_sd(numbers, mean)
        print('Mean:', str(mean))
        print('Standard Deviation:', str(standard_deviation))
        in_file.close()

if __name__ == '__main__':
    obj = Calc_Mean_SD()
    obj.run('random_floats.txt')

# Mean: 3.5
# Standard Deviation: 1.0526157893552612
# http://learningzone.rspsoc.org.uk/index.php/Learning-Materials/Python-Scripting/3.1-Read-and-write-to-text-files