From d89053585e11e869efcc9debb1c311b47b5e20ea Mon Sep 17 00:00:00 2001
From: Jon Dufresne <jon.dufresne@gmail.com>
Date: Fri, 19 Jul 2019 13:55:32 -0700
Subject: [PATCH] Improved error message when index in __getitem__() is
 invalid.

---
 django/core/paginator.py              | 5 ++++-
 django/db/models/query.py             | 5 ++++-
 django/forms/boundfield.py            | 5 ++++-
 tests/forms_tests/tests/test_forms.py | 9 +++++++++
 tests/pagination/tests.py             | 3 ++-
 tests/queries/tests.py                | 5 +++++
 6 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/django/core/paginator.py b/django/core/paginator.py
index d484c31ed5..73dfcd679f 100644
--- a/django/core/paginator.py
+++ b/django/core/paginator.py
@@ -151,7 +151,10 @@ class Page(collections.abc.Sequence):
 
     def __getitem__(self, index):
         if not isinstance(index, (int, slice)):
-            raise TypeError
+            raise TypeError(
+                'Page indices must be integers or slices, not %s.'
+                % type(index).__name__
+            )
         # The object_list is converted to a list so that if it was a QuerySet
         # it won't be a database hit per __getitem__.
         if not isinstance(self.object_list, list):
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 1544beb613..a62947d9d0 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -283,7 +283,10 @@ class QuerySet:
     def __getitem__(self, k):
         """Retrieve an item or slice from the set of results."""
         if not isinstance(k, (int, slice)):
-            raise TypeError
+            raise TypeError(
+                'QuerySet indices must be integers or slices, not %s.'
+                % type(k).__name__
+            )
         assert ((not isinstance(k, slice) and (k >= 0)) or
                 (isinstance(k, slice) and (k.start is None or k.start >= 0) and
                  (k.stop is None or k.stop >= 0))), \
diff --git a/django/forms/boundfield.py b/django/forms/boundfield.py
index 7f40fbbbb4..8832169021 100644
--- a/django/forms/boundfield.py
+++ b/django/forms/boundfield.py
@@ -63,7 +63,10 @@ class BoundField:
         # Prevent unnecessary reevaluation when accessing BoundField's attrs
         # from templates.
         if not isinstance(idx, (int, slice)):
-            raise TypeError
+            raise TypeError(
+                'BoundField indices must be integers or slices, not %s.'
+                % type(idx).__name__
+            )
         return self.subwidgets[idx]
 
     @property
diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index 18fb4a94de..45f5405fee 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -746,6 +746,15 @@ Java</label></li>
             [str(bf[1]), str(bf[2]), str(bf[3])],
         )
 
+    def test_boundfield_invalid_index(self):
+        class TestForm(Form):
+            name = ChoiceField(choices=[])
+
+        field = TestForm()['name']
+        msg = 'BoundField indices must be integers or slices, not str.'
+        with self.assertRaisesMessage(TypeError, msg):
+            field['foo']
+
     def test_boundfield_bool(self):
         """BoundField without any choices (subwidgets) evaluates to True."""
         class TestForm(Form):
diff --git a/tests/pagination/tests.py b/tests/pagination/tests.py
index ef5108e42b..95310d26bd 100644
--- a/tests/pagination/tests.py
+++ b/tests/pagination/tests.py
@@ -366,7 +366,8 @@ class ModelPaginationTests(TestCase):
         # Make sure object_list queryset is not evaluated by an invalid __getitem__ call.
         # (this happens from the template engine when using eg: {% page_obj.has_previous %})
         self.assertIsNone(p.object_list._result_cache)
-        with self.assertRaises(TypeError):
+        msg = 'Page indices must be integers or slices, not str.'
+        with self.assertRaisesMessage(TypeError, msg):
             p['has_previous']
         self.assertIsNone(p.object_list._result_cache)
         self.assertNotIsInstance(p.object_list, list)
diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index c49a0231ac..6d3dcbdb1f 100644
--- a/tests/queries/tests.py
+++ b/tests/queries/tests.py
@@ -2436,6 +2436,11 @@ class QuerySetSupportsPythonIdioms(TestCase):
         with self.assertRaisesMessage(AssertionError, "Negative indexing is not supported."):
             Article.objects.all()[0:-5]
 
+    def test_invalid_index(self):
+        msg = 'QuerySet indices must be integers or slices, not str.'
+        with self.assertRaisesMessage(TypeError, msg):
+            Article.objects.all()['foo']
+
     def test_can_get_number_of_items_in_queryset_using_standard_len(self):
         self.assertEqual(len(Article.objects.filter(name__exact='Article 1')), 1)