diff --git a/web/pgadmin/utils/session.py b/web/pgadmin/utils/session.py
index 9f740f5..0dcca4d 100644
--- a/web/pgadmin/utils/session.py
+++ b/web/pgadmin/utils/session.py
@@ -56,7 +56,15 @@ class ManagedSession(CallbackDict, SessionMixin):
 
     def sign(self, secret):
         if not self.hmac_digest:
-            self.randval = ''.join(random.sample(string.lowercase+string.digits, 20))
+            # If script is running under python2
+            if hasattr(string, 'lowercase'):
+                population = string.lowercase
+            # If script is running under python3
+            elif hasattr(string, 'ascii_lowercase'):
+                population = string.ascii_lowercase
+            population += string.digits
+
+            self.randval = ''.join(random.sample(population, 20))
             self.hmac_digest = _calc_hmac('%s:%s' % (self.sid, self.randval), secret)