I am getting the right answer for the variance , but it still gives me an error which prevents me from moving forward, can some one please tell me why I get this error ? Thanks

```
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(grades)
l = len(scores)
variance = 0
for i in scores:
variance += float(average - i) ** 2
return variance/l
print grades_variance(grades)
```