Custom modelformset returns empty list.

[I159]

I'm writing the custom modelformset. I need that forms to be sorted by value of field "ordering". I overloaded __iter__ and __getitem__ methods of BaseFormSet in my child formset class. 

My code: 

class SortedCatForms(BaseFormSet):

    def __iter__(self):

        print '__iter__'

        return iter(

                sorted(self.forms, key=lambda form: form['ordering'].value()))

        

    def __getitem__(self, index):

        print '__getitem__'

        return self.forms[index]

        

OrderCatsFormSet = modelformset_factory(ParentCategory,

                                        fields=('category', 'ordering'),

                                        formset=SortedCatForms,

                                        extra=0)

OrderCatsFormSet() is empty list. Can't get what the cause of it.

I traced it and have some results:

When I comment out my custom formset it works:

  OrderCatsFormSet = modelformset_factory(ParentCategory,

                                        fields=('category', 'ordering'),

#                                        formset=SortedCatForms,

                                        extra=0)

After, I sorted it and make iterator object:

forms = OrderCatsFormSet().forms

def __iter__():

   ...:     return iter(sorted(forms, key=lambda form: form['ordering'].value()))

for i in __iter__():

   ...:     print i

all my forms is ok...

But when I try to use my modelformset with prints (it is in my code above), __iter__ method not prints.

How to fix it? And, what the cause of the problem? 

Thanks a lot!