def standard_deviation(cls, month):
stats = cls.objects.filter(month_id=month)
total = stats.values_list("rating", flat=True)
N = stats.count()
mean = cls.mean(month)
sum_diff = sum([(mean-float(each))**2 for each in total])
sd = cmath.sqrt(sum_diff / N-1)
return sd.imag * 100
def mean(cls, month):
stats = cls.objects.filter(month_id=month)
total = sum(stats.values_list("rating", flat=True))
N = stats.count()
return total / N
