this is my code:

def grades_variance(scores):

average = grades_average(grades)

variance == 0

for score in scores:

new_average = (average -score) ** 2

variance += new_average

result = variance / float(len(scores))

return result

print grades_variance(scores)

and it gives me an error:

Traceback (most recent call last):

File "python", line 26, in

File "python", line 20, in grades_variance

UnboundLocalError: local variable 'variance' referenced before assignment

I don't know what's wrong, I follow the instructions exactly.