从Django中的基模型实例返回代理模型实例的正确方法?

Say I have models:

说我有模型:

class Animal(models.Model):
    type = models.CharField(max_length=255)

class Dog(Animal):
    def make_sound(self):
        print "Woof!"
    class Meta:
        proxy = True

class Cat(Animal):
    def make_sound(self):
        print "Meow!"
    class Meta:
        proxy = True
class Animal(mode