7. The Variance -- Por Que?


#1

It has to be my order of operations since the definition calculates the value when called, but I can't seem to target where the issue comes from. Suggestions?

ERROR MESSAGE:

Oops, try again. grades_variance([6, 5, 6, 9, 3, 0, 5]) returned 46.8571428571 instead of the expected: 6.693877551

CODE:

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

def print_grades(grades):
    for grade in grades:
        print grade

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)
    variance = 0
    for score in scores:
        variance = variance + ((average - score) ** 2)
        total_variance = variance / len(scores)
    return variance

print grades_variance(grades)

#2

You return varince not total_variance.


#3

Simplifying our statements helps prevent the error pointed out by @eveat.

    for score in scores:
        variance += (average - score) ** 2
    return variance / len(scores)

Or we can write this as a list comprehension:

    return sum([(average - x) ** 2 for x in scores]) / len(scores)

#4

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