Using property in Django - django

Question

I need help with the following situation.
My app has the following models:
class Person(models.Model):
person_sequential_nr = models.IntegerField(primary_key=true)
person_id = models.CharField(max_length=10)
person_name = models.CharField(max_length=200)
year = models.CharField(max_length=4)
#property
def _summarize_goods(self):
return self.goods_set.all().aggregate(Sum('good_value')).values()
patrimony = property(_summarize_goods)
class Goods:
person_sequential_nr = models.Foreignkey()
good_description = models.CharField(max_length=200)
good_value = models.DecimalField(max_digits=12, decimal_places=2)
year = models.CharField(max_length=4)
Year is a string like 2012, 2010, 2008, etc
person_sequential_nr is specific (different) for each year.
person_id is the same for all years.
The intention of _summarize_goods is to totalize all goods of a person in a specific year.
1) How can I get the top ten people with the highest patrimonies?
When I call Person.patrimony it says "TypeError: 'property' object is not callable"
Person._summarize_goods works, but I have no idea how to order it.
2) How can I calculate the patrimony variation from of a person from one year to another (in the past)?
I would like to have something like: variation = (patrimony(year='2012')/patrimony(year='2010') - 1) * 100
I suppose that variation should be also a property, because I would like to use it to order some records.
An additional problem is the the person data may exist in 2012, but may not exist in a year in the past (e.g. 2010). So I need to handle this situation.
3) How can I create a view to show the patrimony of a person?
self.goods_set.all().aggregate(Sum('good_value')) was returning a dictionary, so I added .values() to extract only the values of it, then I got a list.
But wen I use str(Person._summarize_goods) it seemns that I still have a list.
Because when I call:
all_people = Person.objects.all()
people_list = [[p.person_name, str(p._summarize_goods)] for p in all_people]
output = ','.join(people_list)
return HttpResponse(output)
It shows an error referring the line output =
TypeError at /
sequence item 0: expected string, list found
EDITING...
Find some answers:
After removing the decoration (thanks Daniel) Person.patrimony is working so:
1) How can I get the top ten people with the highest patrimonies?
This was solved with the code below:
def ten_highest_pat():
people_2012 = Person.objects.all().filter(year=2012)
return sorted(people_2012, key=lambda person: person.patrimony, reverse=True)[:10]
2) How can I calculate the patrimony variation from of a person from one year to another (in the past)?
I tried the code below, which works, but is too slow. So I would thank you if someone has a sugestion how can I improve it.
def _calc_pat_variation(self):
c = Person.objects.all().filter(person_id = self.person_id, year__lt=self.year).order_by('-year')
if c.count() >= 1 and c[0].patrimony != 0:
return ((self.patrimony / c[0].patrimony) - 1) * 100
else:
return 'Not available'
pat_variation = property(_calc_pat_variation)