diff --git a/dataset/persistence/database.py b/dataset/persistence/database.py
index 8b1a9b5..5a99470 100644
--- a/dataset/persistence/database.py
+++ b/dataset/persistence/database.py
@@ -103,8 +103,9 @@ class Database(object):
         >>> print db.tables
         set([u'user', u'action'])
         """
-        return list(set(self.metadata.tables.keys() +
-                        self._tables.keys()))
+        return list(
+            set(self.metadata.tables.keys()) | set(self._tables.keys())
+        )
 
     def create_table(self, table_name, primary_id='id', primary_type='Integer'):
         """
diff --git a/dataset/persistence/table.py b/dataset/persistence/table.py
index 8c51566..7edb475 100644
--- a/dataset/persistence/table.py
+++ b/dataset/persistence/table.py
@@ -354,7 +354,7 @@ class Table(object):
         Returns the number of rows in the table.
         """
         d = self.database.query(self.table.count()).next()
-        return d.values().pop()
+        return list(d.values()).pop()
 
     def distinct(self, *columns, **_filter):
         """