Added ItemDelta objects and modified replays to make use of them

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40308

scrapy/trunk/scrapy/command/commands/replay.py

@@ -164,24 +164,12 @@ class Command(ScrapyCommand):
         return c, s
 
     def _item_diff(self, old, new):
-        olddic = old.__dict__
-        newdic = new.__dict__
-        ignored_attrs = set(self.opts.ignores or [])
-        allattrs = [a for a in olddic.keys() + newdic.keys() if not a.startswith('_') and a not in ignored_attrs]
-
-        diff = {}
-        for attr in sorted(allattrs):
-            oldval = olddic.get(attr, None)
-            newval = newdic.get(attr, None)
-            if oldval != newval:
-                diff[attr] = {}
-                diff[attr]['old'] = oldval
-                diff[attr]['new'] = newval
+        delta = new - old
 
         s = ""
-        if diff:
+        if delta.diff:
             s += ">>> Item guid=%s name=%s\n" % (old.guid, old.name)
-            s += display.pformat(diff) + "\n"
+            s += display.pformat(delta.diff) + "\n"
         return s
 
     def _format_items(self, items):

scrapy/trunk/scrapy/contrib/item/models.py

@@ -96,7 +96,8 @@ class RobustScrapedItem(ScrapedItem):
             raise AttributeError("Attribute '%s' doesn't exist" % attr)
     
     def __eq__(self, other):
-        return self.version == other.version
+        if other:
+            return self.version == other.version
         
     def __ne__(self, other):
         return self.version != other.version

scrapy/trunk/scrapy/item/models.py

@@ -17,3 +17,27 @@ class ScrapedItem(object):
         value = self.adaptors_pipe.execute(attrname, value)
         if not hasattr(self, attrname):
             setattr(self, attrname, value)
+
+
+class ItemDelta(object):
+    """
+    This class represents the difference between
+    a pair of items.
+    """
+
+    def __init__(self, old, new):
+        self.diff = self.do_diff()
+
+    def do_diff(self):
+        """
+        This method should retreive a dictionary
+        containing the changes between both items
+        as in this example:
+        
+        >>> delta.do_diff()
+        >>> {'attrib': {'new': 'New value', 'old': 'Old value'}, # Common attributes
+             'attrib2': {'new': 'New value 2', 'old': 'Old value 2'},
+             'attrib3': [{'new': 'New list value', 'old': 'Old list value'}, # List attributes
+                         {'new': 'New list value 2', 'old': 'Old list value 2'}]}
+        """
+        pass