Refs #26502 -- Added choices to Form.__getitem__() KeyError message.

django/forms/forms.py

@@ -140,7 +140,12 @@ class BaseForm(object):
             field = self.fields[name]
         except KeyError:
             raise KeyError(
-                "Key %r not found in '%s'" % (name, self.__class__.__name__))
+                "Key '%s' not found in '%s'. Choices are: %s." % (
+                    name,
+                    self.__class__.__name__,
+                    ', '.join(sorted(f for f in self.fields)),
+                )
+            )
         if name not in self._bound_fields_cache:
             self._bound_fields_cache[name] = field.get_bound_field(self, name)
         return self._bound_fields_cache[name]

tests/forms_tests/tests/test_forms.py

@@ -71,10 +71,9 @@ class FormsTestCase(SimpleTestCase):
             '<input type="text" name="birthday" value="1940-10-9" id="id_birthday" />'
         )
 
-        nonexistenterror = "Key u?'nonexistentfield' not found in 'Person'"
-        with six.assertRaisesRegex(self, KeyError, nonexistenterror):
+        msg = "Key 'nonexistentfield' not found in 'Person'. Choices are: birthday, first_name, last_name."
+        with self.assertRaisesMessage(KeyError, msg):
             p['nonexistentfield']
-            self.fail('Attempts to access non-existent fields should fail.')
 
         form_output = []