fixed default adaptor inheritance, added test

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40978

scrapy/trunk/scrapy/contrib_exp/newitem/adaptors.py

@@ -18,8 +18,9 @@ def IDENTITY(v):
 
 class ItemAdaptorMeta(type):
     def __new__(meta, class_name, bases, attrs):
-        da = attrs.get('default_adaptor') or IDENTITY
-        attrs['default_adaptor'] = staticmethod(adaptize(da))
+        da = attrs.get('default_adaptor')
+        if da:
+            attrs['default_adaptor'] = staticmethod(adaptize(da))
 
         cls = type.__new__(meta, class_name, bases, attrs)
 
@@ -46,6 +47,7 @@ class ItemAdaptor(object):
 
     item_class = None
     field_adaptors = {}
+    default_adaptor = IDENTITY
 
     def __init__(self, response=None, item=None):
         self.item_instance = item if item else self.item_class()

scrapy/trunk/scrapy/tests/test_itemadaptor.py

@@ -24,6 +24,9 @@ class TestAdaptor(BaseAdaptor):
 class DefaultedAdaptor(BaseAdaptor):
     default_adaptor = lambda v: v.title()
 
+class InheritDefaultAdaptor(DefaultedAdaptor):
+    pass
+
 
 class ItemAdaptorTest(unittest.TestCase):
 
@@ -39,6 +42,11 @@ class ItemAdaptorTest(unittest.TestCase):
         dta.name = 'marta'
         assert dta.name == 'Marta'
 
+    def test_inheritdefaultadaptor(self):
+        ida = InheritDefaultAdaptor()
+        ida.name = 'marta'
+        assert ida.name == 'Marta'
+
     def test_inheritance(self):
         class ChildTestAdaptor(TestAdaptor):
             url = lambda v: v.lower()