Raise when trying to set an item field value using setattr api, and added tests.

scrapy/item.py

@@ -65,9 +65,15 @@ class DictItem(DictMixin, BaseItem):
 
     def __getattr__(self, name):
         if name in self.fields:
-            raise AttributeError("Use [%r] to access item field value" % name)
+            raise AttributeError("Use item[%r] to get field value" % name)
         raise AttributeError(name)
 
+    def __setattr__(self, name, value):
+        if not name.startswith('_'):
+            raise AttributeError("Use item[%r] = %r to set field value" % \
+                (name, value))
+        super(DictItem, self).__setattr__(name, value)
+
     def keys(self):
         return self._values.keys()
 

scrapy/tests/test_item.py

@@ -71,6 +71,20 @@ class ItemTest(unittest.TestCase):
         i._private = 'test'
         self.assertEqual(i._private, 'test')
 
+    def test_raise_getattr(self):
+        class TestItem(Item):
+            name = Field()
+
+        i = TestItem()
+        self.assertRaises(AttributeError, getattr, i, 'name')
+
+    def test_raise_setattr(self):
+        class TestItem(Item):
+            name = Field()
+
+        i = TestItem()
+        self.assertRaises(AttributeError, setattr, i, 'name', 'john')
+
     def test_custom_methods(self):
         class TestItem(Item):
             name = Field()