Make ``Formset.__getitem__`` O(1), rather than O(n). If you override…

Make ``Formset.__getitem__`` O(1), rather than O(n).  If you override ``__iter__`` you now need to also override ``__getitem__`` for consistant behavior.  Thanks to Carl and Russ for the review.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16770 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/forms/formsets.py

@@ -55,7 +55,7 @@ class BaseFormSet(StrAndUnicode):
 
     def __getitem__(self, index):
         """Returns the form at the given index, based on the rendering order"""
-        return list(self)[index]
+        return self.forms[index]
 
     def __len__(self):
         return len(self.forms)

docs/topics/forms/formsets.txt

@@ -49,6 +49,10 @@ they were created. The default formset iterator also renders the forms
 in this order, but you can change this order by providing an alternate
 implementation for the :meth:`__iter__()` method.
 
+Formsets can also be indexed into, which returns the corresponding form. If you
+override ``__iter__``, you will need to also override ``__getitem__`` to have
+matching behavior.
+
 Using initial data with a formset
 ---------------------------------
 

tests/regressiontests/forms/tests/formsets.py

@@ -793,8 +793,10 @@ class FormsFormsetTestCase(TestCase):
         # Formets can override the default iteration order
         class BaseReverseFormSet(BaseFormSet):
             def __iter__(self):
-                for form in reversed(self.forms):
-                    yield form
+                return reversed(self.forms)
+
+            def __getitem__(self, idx):
+                return super(BaseReverseFormSet, self).__getitem__(len(self) - idx - 1)
 
         ReverseChoiceFormset = formset_factory(Choice, BaseReverseFormSet, extra=3)
         reverse_formset = ReverseChoiceFormset()
@@ -911,12 +913,12 @@ class TestIsBoundBehavior(TestCase):
         # The empty forms should be equal.
         self.assertEqual(empty_forms[0].as_p(), empty_forms[1].as_p())
 
-class TestEmptyFormSet(TestCase): 
+class TestEmptyFormSet(TestCase):
     "Test that an empty formset still calls clean()"
-    def test_empty_formset_is_valid(self): 
-        EmptyFsetWontValidateFormset = formset_factory(FavoriteDrinkForm, extra=0, formset=EmptyFsetWontValidate) 
-        formset = EmptyFsetWontValidateFormset(data={'form-INITIAL_FORMS':'0', 'form-TOTAL_FORMS':'0'},prefix="form") 
-        formset2 = EmptyFsetWontValidateFormset(data={'form-INITIAL_FORMS':'0', 'form-TOTAL_FORMS':'1', 'form-0-name':'bah' },prefix="form") 
-        self.assertFalse(formset.is_valid()) 
-        self.assertFalse(formset2.is_valid()) 
+    def test_empty_formset_is_valid(self):
+        EmptyFsetWontValidateFormset = formset_factory(FavoriteDrinkForm, extra=0, formset=EmptyFsetWontValidate)
+        formset = EmptyFsetWontValidateFormset(data={'form-INITIAL_FORMS':'0', 'form-TOTAL_FORMS':'0'},prefix="form")
+        formset2 = EmptyFsetWontValidateFormset(data={'form-INITIAL_FORMS':'0', 'form-TOTAL_FORMS':'1', 'form-0-name':'bah' },prefix="form")
+        self.assertFalse(formset.is_valid())
+        self.assertFalse(formset2.is_valid())