It returns a result not divided by length every time, and i can't understand why variance == variance /len(scores) doesn't work correcly

for example one of error messages is:

Oops, try again. grades_variance([6, 7, 2]) returned 14.0 instead of the expected: 4.6666666667

```
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 += (average - score) ** 2
return variance
variance == variance /len(scores)
return variance
print grades_variance(grades)
```