exam grade statistics | Python Fiddle

def print_grades(grades):
    for index, grade in enumerate(grades):
        print "{:3d}. :  {:5.1f}".format(index, grade)  ## formatting does not really work as the output field does not support a monospaced font

def grades_sum(grades):
    total = 0
    for grade in grades: 
        total += grade
    return total
    
def grades_average(grades):
    sum_of_grades = grades_sum(grades)
    average = sum_of_grades / float(len(grades))
    return average

def grades_variance(scores):
    average = grades_average(scores)
    ssquares = 0;
    for score in scores:
        ssquares += (average - score) ** 2 ## sum of squared difference of each score from the average score
    return ssquares / float(len(scores))   ## variance
    
def grades_std_deviation(variance):
    return variance ** 0.5                 ## square root

##
grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]

print_grades(grades)
print "sum ........ : ", "{:0.3f}".format(grades_sum(grades)) ## displayed with 3 decimals
print "mean ....... : ", grades_average(grades)
print "variance ... : ", grades_variance(grades)
print "std ........ : ", grades_std_deviation(grades_variance(grades))

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