diff --git a/gc3libs/persistence/idfactory.py b/gc3libs/persistence/idfactory.py
old mode 100644
new mode 100755
index 15bac2bf..0d192113
--- a/gc3libs/persistence/idfactory.py
+++ b/gc3libs/persistence/idfactory.py
@@ -2,7 +2,7 @@
 #
 """
 """
-# Copyright (C) 2011 S3IT, Zentrale Informatik, University of Zurich. All rights reserved.
+# Copyright (C) 2011, 2018 University of Zurich. All rights reserved.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU Lesser General Public License as published by
@@ -121,10 +121,7 @@ def __init__(self, prefix=None, next_id_fn=None, id_class=Id):
         (which is the one used by default).
         """
         self._prefix = prefix
-        if next_id_fn is None:
-            self._next_id_fn = progressive_number
-        else:
-            self._next_id_fn = next_id_fn
+        self._next_id_fn = next_id_fn or progressive_number
         self._idclass = id_class
 
     def reserve(self, n):
@@ -142,11 +139,8 @@ def new(self, obj):
         """
         Return a new "unique identifier" instance (a string).
         """
-        if self._prefix is None:
-            prefix = obj.__class__.__name__
-        else:
-            prefix = self._prefix
-        if len(IdFactory._seqno_pool) > 0:
+        prefix = self._prefix or obj.__class__.__name__
+        if IdFactory._seqno_pool:
             seqno = IdFactory._seqno_pool.pop()
         else:
             seqno = self._next_id_fn()
diff --git a/gc3libs/persistence/sql.py b/gc3libs/persistence/sql.py
index 8a0863ac..3d45850d 100755
--- a/gc3libs/persistence/sql.py
+++ b/gc3libs/persistence/sql.py
@@ -133,10 +133,7 @@ def __init__(self, url, table_name=None, idfactory=None,
             kv = {}
 
         # init static public args
-        if not idfactory:
-            self.idfactory = IdFactory(id_class=IntId)
-        else:
-            self.idfactory = idfactory
+        self.idfactory = idfactory or IdFactory(id_class=IntId)
 
         url_table_names = kv.get('table')
         if url_table_names: