Add basic support for AttributeUpdates in Dynamo update_item. Closes #449.

tests/test_dynamodb2/test_dynamodb_table_without_range_key.py

@@ -122,6 +122,33 @@ def test_item_add_and_describe_and_update():
     })
 
 
+@requires_boto_gte("2.9")
+@mock_dynamodb2
+def test_item_partial_save():
+    table = create_table()
+
+    data = {
+        'forum_name': 'LOLCat Forum',
+        'Body': 'http://url_to_lolcat.gif',
+        'SentBy': 'User A',
+    }
+
+    table.put_item(data=data)
+    returned_item = table.get_item(forum_name="LOLCat Forum")
+
+    returned_item['SentBy'] = 'User B'
+    returned_item.partial_save()
+
+    returned_item = table.get_item(
+        forum_name='LOLCat Forum'
+    )
+    dict(returned_item).should.equal({
+        'forum_name': 'LOLCat Forum',
+        'Body': 'http://url_to_lolcat.gif',
+        'SentBy': 'User B',
+    })
+
+
 @requires_boto_gte("2.9")
 @mock_dynamodb2
 def test_item_put_without_table():