[Answered ]-Django objects queryset

First, you can get the list of decimals directly by using values_list

qs = Foo.objects.order_by('date').values_list('amount', flat=True)

Secondly, if it is easier to calculate SD on floats, rather than on a list of decimals, you can do

qs = Foo.objects.order_by('date').values_list('amount', flat=True)
float_qs = map(float, qs)