diff --git a/tiramisu/log.py b/tiramisu/log.py
index 06ca676..31aae0a 100644
--- a/tiramisu/log.py
+++ b/tiramisu/log.py
@@ -15,9 +15,16 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 # ____________________________________________________________
-from logging import getLogger
+from logging import getLogger, DEBUG, basicConfig, StreamHandler, Formatter
+import os
 
 
 log = getLogger('tiramisu')
-# import logging
-# logging.basicConfig(format='%(levelname)s:%(message)s', level=logging.DEBUG)
+if os.environ.get('TIRAMISU_DEBUG') == 'True':
+    log.setLevel(DEBUG)
+    handler = StreamHandler()
+    handler.setLevel(DEBUG)
+    formatter = Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
+    handler.setFormatter(formatter)
+
+    log.addHandler(handler)
diff --git a/tiramisu/storage/dictionary/setting.py b/tiramisu/storage/dictionary/setting.py
index ab50383..d835683 100644
--- a/tiramisu/storage/dictionary/setting.py
+++ b/tiramisu/storage/dictionary/setting.py
@@ -32,16 +32,16 @@ class Properties(Cache):
 
     # properties
     def setproperties(self, path, properties):
-        log.debug('setproperties', path, properties)
+        log.debug('setproperties %s %s', path, properties)
         self._properties[path] = properties
 
     def getproperties(self, path, default_properties):
         ret = self._properties.get(path, frozenset(default_properties))
-        log.debug('getproperties', path, ret)
+        log.debug('getproperties %s %s', path, ret)
         return ret
 
     def delproperties(self, path):
-        log.debug('delproperties', path)
+        log.debug('delproperties %s', path)
         if path in self._properties:
             del(self._properties[path])
 
@@ -64,7 +64,7 @@ class Permissives(Cache):
         super(Permissives, self).__init__(storage)
 
     def setpermissives(self, path, permissives):
-        log.debug('setpermissives', path, permissives)
+        log.debug('setpermissives %s %s', path, permissives)
         if not permissives:
             if path in self._permissives:
                 del self._permissives[path]
@@ -73,7 +73,7 @@ class Permissives(Cache):
 
     def getpermissives(self, path=None):
         ret = self._permissives.get(path, frozenset())
-        log.debug('getpermissives', path, ret)
+        log.debug('getpermissives %s %s', path, ret)
         return ret
 
     def exportation(self):
@@ -86,6 +86,6 @@ class Permissives(Cache):
         self._permissives = permissives
 
     def delpermissive(self, path):
-        log.debug('delpermissive', path)
+        log.debug('delpermissive %s', path)
         if path in self._permissives:
             del(self._permissives[path])
diff --git a/tiramisu/storage/dictionary/value.py b/tiramisu/storage/dictionary/value.py
index c2fe821..360a273 100644
--- a/tiramisu/storage/dictionary/value.py
+++ b/tiramisu/storage/dictionary/value.py
@@ -76,7 +76,7 @@ class Values(Cache):
         """set value for a path
         a specified value must be associated to an owner
         """
-        log.debug('setvalue', path, value, owner, index, id(self))
+        log.debug('setvalue %s %s %s %s %s', path, value, owner, index, id(self))
         values = []
         vidx = None
 
@@ -97,7 +97,7 @@ class Values(Cache):
         return: boolean
         """
         has_path = path in self._values[0]
-        log.debug('hasvalue', path, index, has_path, id(self))
+        log.debug('hasvalue %s %s %s %s', path, index, has_path, id(self))
         if index is None:
             return has_path
         elif has_path:
@@ -110,7 +110,7 @@ class Values(Cache):
         """
         _values == ((path1, path2), ((idx1_1, idx1_2), None), ((value1_1, value1_2), value2), ((owner1_1, owner1_2), owner2))
         """
-        log.debug('reduce_index', path, index, id(self))
+        log.debug('reduce_index %s %s %s', path, index, id(self))
         path_idx = self._values[0].index(path)
         # get the "index" position
         subidx = self._values[1][path_idx].index(index)
@@ -129,7 +129,7 @@ class Values(Cache):
                          path,
                          index,
                          commit):
-        log.debug('resetvalue_index', path, index, id(self))
+        log.debug('resetvalue_index %s %s %s', path, index, id(self))
         def _resetvalue(nb):
             values_idx = list(values[nb])
             del(values_idx[path_idx])
@@ -163,7 +163,7 @@ class Values(Cache):
                    commit):
         """remove value means delete value in storage
         """
-        log.debug('resetvalue', path, id(self))
+        log.debug('resetvalue %s %s', path, id(self))
         def _resetvalue(nb):
             lst = list(self._values[nb])
             lst.pop(idx)
@@ -216,7 +216,7 @@ class Values(Cache):
                                       with_value)
         if owner is undefined:
             owner = default
-        log.debug('getvalue', path, index, value, owner, id(self))
+        log.debug('getvalue %s %s %s %s %s', path, index, value, owner, id(self))
         if with_value:
             return owner, value
         else:
diff --git a/tiramisu/storage/sqlite3/setting.py b/tiramisu/storage/sqlite3/setting.py
index 448766d..cce1445 100644
--- a/tiramisu/storage/sqlite3/setting.py
+++ b/tiramisu/storage/sqlite3/setting.py
@@ -81,7 +81,7 @@ class Permissives(Sqlite3DB):
     # permissive
     def setpermissives(self, path, permissive):
         path = self._sqlite_encode_path(path)
-        log.debug('setpermissive', path, permissive, id(self))
+        log.debug('setpermissive %s %s %s', path, permissive, id(self))
         self._storage.execute("DELETE FROM permissive WHERE path = ? AND session_id = ?",
                               (path, self._session_id),
                               False)
@@ -99,7 +99,7 @@ class Permissives(Sqlite3DB):
             ret = frozenset()
         else:
             ret = frozenset(self._sqlite_decode(permissives[0]))
-        log.debug('getpermissive', path, ret, id(self))
+        log.debug('getpermissive %s %s %s', path, ret, id(self))
         return ret
 
     def delpermissive(self, path):
diff --git a/tiramisu/storage/sqlite3/value.py b/tiramisu/storage/sqlite3/value.py
index 0aa8b44..b35c64e 100644
--- a/tiramisu/storage/sqlite3/value.py
+++ b/tiramisu/storage/sqlite3/value.py
@@ -54,7 +54,7 @@ class Values(Sqlite3DB):
         """set value for an option
         a specified value must be associated to an owner
         """
-        log.debug('setvalue', path, value, owner, index, commit)
+        log.debug('setvalue %s %s %s %s %s', path, value, owner, index, commit)
         path = self._sqlite_encode_path(path)
         if index is not None:
             self.resetvalue_index(path,
@@ -81,7 +81,7 @@ class Values(Sqlite3DB):
         """if opt has a value
         return: boolean
         """
-        log.debug('hasvalue', path, index)
+        log.debug('hasvalue %s %s', path, index)
         path = self._sqlite_encode_path(path)
         return self._sqlite_select(path, index) is not None
 
@@ -91,7 +91,7 @@ class Values(Sqlite3DB):
         _values == ((path1, path2), ((idx1_1, idx1_2), None),
                     ((value1_1, value1_2), value2), ((owner1_1, owner1_2), owner2))
         """
-        log.debug('reduce_index', path, index, id(self))
+        log.debug('reduce_index %s %s %s', path, index, id(self))
         self._storage.execute("UPDATE value SET idx = ? WHERE path = ? and idx = ? "
                               "AND session_id = ?",
                               (index - 1, path, index, self._session_id))
@@ -102,7 +102,7 @@ class Values(Sqlite3DB):
                          commit=True):
         """remove value means delete value in storage
         """
-        log.debug('resetvalue_index', path, index, commit)
+        log.debug('resetvalue_index %s %s %s', path, index, commit)
         path = self._sqlite_encode_path(path)
         self._storage.execute("DELETE FROM value WHERE path = ? AND session_id = ? AND idx = ?",
                               (path, self._session_id, index),
@@ -113,7 +113,7 @@ class Values(Sqlite3DB):
                    commit):
         """remove value means delete value in storage
         """
-        log.debug('resetvalue', path, commit)
+        log.debug('resetvalue %s %s', path, commit)
         path = self._sqlite_encode_path(path)
         self._storage.execute("DELETE FROM value WHERE path = ? AND session_id = ?",
                               (path, self._session_id),
@@ -126,7 +126,7 @@ class Values(Sqlite3DB):
                  index=None):
         """change owner for an option
         """
-        log.debug('setowner', path, owner, index)
+        log.debug('setowner %s %s %s', path, owner, index)
         path = self._sqlite_encode_path(path)
         if index is None:
             self._storage.execute("UPDATE value SET owner = ? WHERE path = ? AND session_id = ?",
@@ -143,7 +143,7 @@ class Values(Sqlite3DB):
         """get owner for an option
         return: owner object
         """
-        log.debug('getowner', path, default, index, with_value)
+        log.debug('getowner %s %s %s %s', path, default, index, with_value)
         path = self._sqlite_encode_path(path)
         request = "SELECT owner, value FROM value WHERE path = ? AND session_id = ?"
         if index is not None:
@@ -178,7 +178,7 @@ class Values(Sqlite3DB):
         :param key: information's key (ex: "help", "doc"
         :param value: information's value (ex: "the help string")
         """
-        log.debug('set_information', key, value)
+        log.debug('set_information %s %s', key, value)
         path = self._sqlite_encode_path(path)
         self._storage.execute("DELETE FROM information WHERE key = ? AND session_id = ? AND path = ?",
                              (key, self._session_id, path),
@@ -191,7 +191,7 @@ class Values(Sqlite3DB):
 
         :param key: the item string (ex: "help")
         """
-        log.debug('get_information', key, default)
+        log.debug('get_information %s %s', key, default)
         path = self._sqlite_encode_path(path)
         value = self._storage.select("SELECT value FROM information WHERE key = ? AND "
                                      "session_id = ? AND path = ?",
@@ -205,7 +205,7 @@ class Values(Sqlite3DB):
             return self._sqlite_decode(value[0])
 
     def del_information(self, path, key, raises):
-        log.debug('del_information', key, raises)
+        log.debug('del_information %s %s', key, raises)
         path = self._sqlite_encode_path(path)
         if raises and self._storage.select("SELECT value FROM information WHERE key = ? "
                                            "AND session_id = ? AND path = ?",
@@ -282,7 +282,7 @@ class Values(Sqlite3DB):
 
     def get_max_length(self,
                        path):
-        log.debug('get_max_length', path)
+        log.debug('get_max_length %s', path)
         val_max = self._storage.select("SELECT max(idx) FROM value WHERE path = ? AND session_id = ?",
                                        (path, self._session_id), False)
         if val_max[0][0] is None:
diff --git a/tiramisu/storage/util.py b/tiramisu/storage/util.py
index 33ce22f..2d990ff 100644
--- a/tiramisu/storage/util.py
+++ b/tiramisu/storage/util.py
@@ -75,16 +75,16 @@ class Cache(DictCache):
                          'expire' in self_props):
                     ntime = int(time())
                     if timestamp + expiration_time >= ntime:
-                        log.debug('getcache in cache (1)', path, value, _display_classname(self),
+                        log.debug('getcache in cache (1) %s %s %s %s %s', path, value, _display_classname(self),
                                   id(self), index)
                         return True, value
-                    else:
-                        log.debug('getcache expired value for path {} < {}'.format(
-                                  timestamp + expiration_time, ntime))
-                        # if expired, remove from cache
-                        #self.delcache(path)
+                    #else:
+                    #    log.debug('getcache expired value for path {} < {}'.format(
+                    #              timestamp + expiration_time, ntime))
+                    #    # if expired, remove from cache
+                    #    #self.delcache(path)
                 else:
-                    log.debug('getcache in cache (2)', path, value, _display_classname(self),
+                    log.debug('getcache in cache (2) %s %s %s %s %s', path, value, _display_classname(self),
                               id(self), index)
                     return True, value
         log.debug('getcache {} with index {} not in {} cache'.format(path, index,
@@ -94,13 +94,13 @@ class Cache(DictCache):
     def delcache(self, path):
         """remove cache for a specified path
         """
-        log.debug('delcache', path, _display_classname(self), id(self))
+        log.debug('delcache %s %s %s', path, _display_classname(self), id(self))
         if path in  self._cache:
             self._delcache(path)
 
     def reset_all_cache(self):
         "empty the cache"
-        log.debug('reset_all_cache', _display_classname(self), id(self))
+        log.debug('reset_all_cache %s %s', _display_classname(self), id(self))
         self._reset_all_cache()
 
     def get_cached(self):