Hi, this code works, but I get an error message!!!!! The error message gives me this:

```
Oops, try again.
It looks like not all grades were printed! Make sure you are printing ech one on their own line.
```

THIS IS MY 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

numerator = 0

for score in scores:

numerator += (average - score) ** 2

variance = numerator / float(len(scores))

return variance

def grades_std_deviation(variance):

return float(variance) ** 0.5

print grades

print grades_sum(grades)

print grades_average(grades)

print grades_variance(grades)

print grades_std_deviation(grades_variance(grades))

THIS IS MY OUTPUT:

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

1045.5

80.4230769231

334.071005917

18.2776094147

None

can you please help me understand what is going on?