trackref Libxml2Document objects and do not silence xml exceptions on __del__

scrapy/selector/document.py

@@ -5,9 +5,10 @@ garbage collection to libxml2 documents (xmlDoc).
 
 import weakref
 
+from scrapy.utils.trackref import object_ref
 from .factories import xmlDoc_from_html
 
-class Libxml2Document(object):
+class Libxml2Document(object_ref):
 
     cache = weakref.WeakKeyDictionary()
     __slots__ = ['xmlDoc', 'xpathContext', '__weakref__']
@@ -15,7 +16,7 @@ class Libxml2Document(object):
     def __new__(cls, response, factory=xmlDoc_from_html):
         cache = cls.cache.setdefault(response, {})
         if factory not in cache:
-            obj = object.__new__(cls)
+            obj = object_ref.__new__(cls)
             obj.xmlDoc = factory(response)
             obj.xpathContext = obj.xmlDoc.xpathNewContext()
             cache[factory] = obj
@@ -29,12 +30,8 @@ class Libxml2Document(object):
         # TypeError, so the try/except block silences them
         try:
             self.xmlDoc.freeDoc()
-        except:
-            pass
-        try:
+        finally:
             self.xpathContext.xpathFreeContext()
-        except:
-            pass
 
     def __str__(self):
         return "<Libxml2Document %s>" % self.xmlDoc.name