Fixed #35766 -- Handled slices in BaseChoiceIterator.

django/utils/choices.py

@@ -21,8 +21,9 @@ def __eq__(self, other):
         return super().__eq__(other)
 
     def __getitem__(self, index):
-        if index < 0:
-            # Suboptimally consume whole iterator to handle negative index.
+        if isinstance(index, slice) or index < 0:
+            # Suboptimally consume whole iterator to handle slices and negative
+            # indexes.
             return list(self)[index]
         try:
             return next(islice(self, index, index + 1))

tests/model_fields/tests.py

@@ -183,6 +183,33 @@ def test_choices(self):
             self.choices_from_callable.choices.func(), [(0, "0"), (1, "1"), (2, "2")]
         )
 
+    def test_choices_slice(self):
+        for choices, expected_slice in [
+            (self.empty_choices.choices, []),
+            (self.empty_choices_bool.choices, []),
+            (self.empty_choices_text.choices, []),
+            (self.with_choices.choices, [(1, "A")]),
+            (self.with_choices_dict.choices, [(1, "A")]),
+            (self.with_choices_nested_dict.choices, [("Thing", [(1, "A")])]),
+            (self.choices_from_iterator.choices, [(0, "0"), (1, "1")]),
+            (self.choices_from_callable.choices.func(), [(0, "0"), (1, "1")]),
+            (self.choices_from_callable.choices, [(0, "0"), (1, "1")]),
+        ]:
+            with self.subTest(choices=choices):
+                self.assertEqual(choices[:2], expected_slice)
+
+    def test_choices_negative_index(self):
+        for choices, expected_choice in [
+            (self.with_choices.choices, (1, "A")),
+            (self.with_choices_dict.choices, (1, "A")),
+            (self.with_choices_nested_dict.choices, ("Thing", [(1, "A")])),
+            (self.choices_from_iterator.choices, (2, "2")),
+            (self.choices_from_callable.choices.func(), (2, "2")),
+            (self.choices_from_callable.choices, (2, "2")),
+        ]:
+            with self.subTest(choices=choices):
+                self.assertEqual(choices[-1], expected_choice)
+
     def test_flatchoices(self):
         self.assertEqual(self.no_choices.flatchoices, [])
         self.assertEqual(self.empty_choices.flatchoices, [])