allow to override item class adaptor in constructor

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40277

scrapy/trunk/scrapy/item/models.py

@@ -3,8 +3,15 @@ from scrapy.item.adaptors import AdaptorPipe
 class ScrapedItem(object):
     """
     This is the base class for all scraped items.
+    'guid' attribute is required, and is an attribute
+    that identifies uniquely the given scraped item.
     """
-    adaptors_pipe = AdaptorPipe([])
+    adaptors_pipe = AdaptorPipe()
+
+    def __init__(self, adaptors_pipe=None):
+        """If an adaptors_pipe is given, overrides class adaptors_pipe"""
+        if adaptors_pipe:
+            self.adaptors_pipe = adaptors_pipe
 
     def attribute(self, attrname, value):
         value = self.adaptors_pipe.execute(attrname, value)