Django models, custom functions

What you probably want is a custom manager

From the django docs:

        # An example of a custom manager called "objects".

class PersonManager(models.Manager):
    def get_fun_people(self):
        return self.filter(fun=True)

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    fun = models.BooleanField()
    objects = PersonManager()

    def __unicode__(self):
        return u"%s %s" % (self.first_name, self.last_name)

which then allows you to do something like:

>>> p1 = Person(first_name="Bugs", last_name="Bunny", fun=True)
>>> p1.save()
>>> p2 = Person(first_name="Droopy", last_name="Dog", fun=False)
>>> p2.save()
>>> Person.objects.get_fun_people()
[<Person: Bugs Bunny>]