Fix _metadict to allow removing un hashable value.

theano/gof/opt.py

@@ -380,9 +380,12 @@ class _metadict:
             self.l.append((item, value))
 
     def __delitem__(self, item):
+        try:
             if item in self.d:
                 del self.d[item]
-        else:
+                return
+        except TypeError, e:
+            assert "unhashable type" in str(e)
         for i, (key, val) in enumerate(self.l):
             if key == item:
                 del self.l[i]
@@ -390,9 +393,12 @@ class _metadict:
             raise KeyError(item)
 
     def discard(self, item):
+        try:
             if item in self.d:
                 del self.d[item]
-        else:
+                return
+        except TypeError, e:
+            assert "unhashable type" in str(e)
         for i, (key, val) in enumerate(self.l):
             if key == item:
                 del self.l[i]