"The Varience" - wrong result in grades_varience



When I run my code as part of the lesson I get
**Oops, try again.
grades_variance([9, 5]) returned 0.6153846154 instead of the expected: 4.0

When I run it in Codecademy Labs (Python) I get the answer that the lesson says it was expecting (so in the above example if I run it with [9,5] I get the correct answer of 4.0 , not what the lesson says it got running it for me (0.6153846154).

I don't get why I seem to be getting two different results with exactly the same code, both running in different places in Codeecademy.

Can anyone see where I'm going wrong (and thanks for taking to time to help or to try to help) ?

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

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

def grades_variance(scores):
    average = grades_average(scores)
    variance = 0
    for score in scores:
        print (average - score) ** 2
        variance += ((average - score) ** 2)
        print variance
    answer = variance / float(len(grades))
    print answer
    return answer
print grades_variance(grades)


Here you need to use len(scores) not len(grades).


You were absolutely right !
Thanks for the help, all the best.


A side note:

When faced with a choice between making a computed value or a counting number into a float, choose the computed value and leave the counting number as an integer.

float(sum_of_grades) / len(grades)             # yields a float

    variance += float(average - score) ** 2    # variance is a float

return variance / len(scores)                  # a float value is returned

This all can trace back to the grades list and the grades_sum() function. That the point at which to define the floats.

total += float(grade)                          # total will be a float

After that we no longer need to set a float anywhere else in the program. In truth, even the above is not necessary except for explicitness. The last value in the list is a float so even if total is an integer, adding that value will switch it to a float.


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