diff --git a/test/test_config.py b/test/test_config.py
index 80b1b66..5e76886 100644
--- a/test/test_config.py
+++ b/test/test_config.py
@@ -165,6 +165,9 @@ def test_information_config():
     assert config.impl_get_information('info') == string
     raises(ValueError, "config.impl_get_information('noinfo')")
     assert config.impl_get_information('noinfo', 'default') == 'default'
+    config.impl_del_information('info')
+    raises(ValueError, "config.impl_get_information('info')")
+    raises(ValueError, "config.impl_del_information('noinfo')")
 
 
 def test_config_impl_get_path_by_opt():
diff --git a/test/test_config_api.py b/test/test_config_api.py
index b96607a..eeaf275 100644
--- a/test/test_config_api.py
+++ b/test/test_config_api.py
@@ -162,6 +162,10 @@ def test_find_in_config():
     ret = conf.find(byname='dummy')
     assert len(ret) == 1
     _is_same_opt(ret[0], conf.unwrap_from_path('gc.dummy'))
+    #
+    ret = conf.find_first(byname='dummy')
+    _is_same_opt(ret, conf.unwrap_from_path('gc.dummy'))
+    #
     ret = conf.find(byname='float')
     assert len(ret) == 2
     _is_same_opt(ret[0], conf.unwrap_from_path('gc.float'))
diff --git a/test/test_duplicate_config.py b/test/test_duplicate_config.py
index ce3dd3a..ccc45aa 100644
--- a/test/test_duplicate_config.py
+++ b/test/test_duplicate_config.py
@@ -61,8 +61,8 @@ def test_duplicate_force_store_value():
     descr = make_description()
     conf = Config(descr)
     conf2 = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'creole.general.wantref': ('forced', False)}
-    assert conf2.cfgimpl_get_values()._p_.get_modified_values() == {'creole.general.wantref': ('forced', False)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'creole.general.wantref': ('forced', False)}
+    assert conf2.cfgimpl_get_values().get_modified_values() == {'creole.general.wantref': ('forced', False)}
     conf.creole.general.wantref = True
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'creole.general.wantref': ('user', True)}
-    assert conf2.cfgimpl_get_values()._p_.get_modified_values() == {'creole.general.wantref': ('forced', False)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'creole.general.wantref': ('user', True)}
+    assert conf2.cfgimpl_get_values().get_modified_values() == {'creole.general.wantref': ('forced', False)}
diff --git a/test/test_dyn_optiondescription.py b/test/test_dyn_optiondescription.py
index 12d45b3..254acf4 100644
--- a/test/test_dyn_optiondescription.py
+++ b/test/test_dyn_optiondescription.py
@@ -646,6 +646,7 @@ def test_find_dyndescription_context():
     assert isinstance(cfg.find_first(byname='stval1', type_='option'), DynSymLinkOption)
     assert cfg.find(bytype=StrOption, type_='path') == ['od.dodval1.stval1', 'od.dodval2.stval2', 'od.val1']
     opts = cfg.find(byvalue='yes')
+    raises(AttributeError, "cfg.find(byname='strnotexists')")
     assert len(opts) == 1
     assert isinstance(opts[0], DynSymLinkOption)
     assert opts[0].impl_getname() == 'stval1'
diff --git a/test/test_freeze.py b/test/test_freeze.py
index eeff973..504cda6 100644
--- a/test/test_freeze.py
+++ b/test/test_freeze.py
@@ -170,15 +170,15 @@ def test_freeze_get_multi():
 def test_force_store_value():
     descr = make_description_freeze()
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'wantref': ('forced', False),
+    assert conf.cfgimpl_get_values().get_modified_values() == {'wantref': ('forced', False),
                                                                    'wantref2': ('forced', False),
                                                                    'wantref3': ('forced', (False,))}
     conf.wantref = True
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'wantref': ('user', True),
+    assert conf.cfgimpl_get_values().get_modified_values() == {'wantref': ('user', True),
                                                                    'wantref2': ('forced', False),
                                                                    'wantref3': ('forced', (False,))}
     del(conf.wantref)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'wantref': ('forced', False),
+    assert conf.cfgimpl_get_values().get_modified_values() == {'wantref': ('forced', False),
                                                                    'wantref2': ('forced', False),
                                                                    'wantref3': ('forced', (False,))}
 
@@ -206,28 +206,28 @@ def test_force_store_value_masterslaves():
     descr = OptionDescription("int", "", [b, c])
     descr.impl_set_group_type(groups.master)
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'int': ('forced', ())}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'int': ('forced', ())}
 
 
 def test_force_store_value_callback():
     b = IntOption('int', 'Test int option', properties=('force_store_value',), callback=return_val)
     descr = OptionDescription("int", "", [b])
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'int': ('forced', 1)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'int': ('forced', 1)}
 
 
 def test_force_store_value_callback_params():
     b = IntOption('int', 'Test int option', properties=('force_store_value',), callback=return_val2, callback_params={'value': (2,)})
     descr = OptionDescription("int", "", [b])
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'int': ('forced', 2)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'int': ('forced', 2)}
 
 
 def test_force_store_value_callback_params_2():
     b = IntOption('int', 'Test int option', properties=('force_store_value',), callback=return_val3, callback_params={'': ((None,),), 'value': (2,)})
     descr = OptionDescription("int", "", [b])
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'int': ('forced', 2)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'int': ('forced', 2)}
 
 
 def test_force_store_value_callback_params_with_opt():
@@ -235,4 +235,4 @@ def test_force_store_value_callback_params_with_opt():
     b = IntOption('int', 'Test int option', properties=('force_store_value',), callback=return_val2, callback_params={'value': ((a, False),)})
     descr = OptionDescription("int", "", [a, b])
     conf = Config(descr)
-    assert conf.cfgimpl_get_values()._p_.get_modified_values() == {'int': ('forced', 2)}
+    assert conf.cfgimpl_get_values().get_modified_values() == {'int': ('forced', 2)}
diff --git a/test/test_option.py b/test/test_option.py
index bbe88a1..5c2fc25 100644
--- a/test/test_option.py
+++ b/test/test_option.py
@@ -14,38 +14,6 @@ def a_func():
     return None
 
 
-#def test_option_comparison():
-#    "compare :class:`tiramisu.option.BoolOption`"
-#    dummy1 = BoolOption('dummy1', 'doc dummy')
-#    dummy2 = BoolOption('dummy2', 'doc dummy')
-#    dummy3 = BoolOption('dummy1', 'doc dummy')
-#    assert dummy1 != dummy2
-#    assert dummy1 == dummy3
-
-
-#def test_option_comparison_obj():
-#    "compare :class:`tiramisu.option.IntOption`"
-#    dummy1 = BoolOption('dummy1', 'doc dummy')
-#    dummy2 = IntOption('dummy1', 'doc dummy')
-#    assert dummy1 != dummy2
-
-
-#def test_option_comparison_advanced():
-#    dummy1 = BoolOption('dummy1', 'doc dummy')
-#    dummy2 = BoolOption('dummy1', 'doc dummy')
-#    dummy3 = BoolOption('dummy1', 'doc dummy', None)
-#    dummy4 = BoolOption('dummy1', 'doc dummy', True)
-#    dummy5 = BoolOption('dummy1', 'doc dummy', multi=True)
-#    dummy6 = BoolOption('dummy1', 'doc dummy', properties=tuple())
-#    dummy7 = BoolOption('dummy1', 'doc dummy', properties=tuple('new',))
-#    assert dummy1 == dummy2
-#    assert dummy1 == dummy3
-#    assert dummy1 != dummy4
-#    assert dummy1 != dummy5
-#    assert dummy1 == dummy6
-#    assert dummy1 != dummy7
-
-
 def test_option_valid_name():
     IntOption('test', '')
     raises(ValueError, 'IntOption(1, "")')
@@ -62,61 +30,61 @@ def test_option_with_callback():
     raises(ValueError, "IntOption('test', '', default=1, callback=a_func)")
 
 
-#def test_option_get_information():
-#    description = "it's ok"
-#    string = 'some informations'
-#    i = IntOption('test', description)
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    i.impl_set_information('info', string)
+def test_option_get_information():
+    description = "it's ok"
+    string = 'some informations'
+    i = IntOption('test', description)
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    i.impl_set_information('info', string)
+    assert i.impl_get_information('info') == string
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    assert i.impl_get_information('noinfo', 'default') == 'default'
+    assert i.impl_get_information('doc') == description
+    assert i.impl_getdoc() == description
+
+
+def test_option_get_information_config():
+    description = "it's ok"
+    string = 'some informations'
+    string
+    i = IntOption('test', description)
+    od = OptionDescription('od', '', [i])
+    Config(od)
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    raises(AttributeError, "i.impl_set_information('info', string)")
 #    assert i.impl_get_information('info') == string
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    assert i.impl_get_information('noinfo', 'default') == 'default'
-#    assert i.impl_get_information('doc') == description
-#    assert i.impl_getdoc() == description
-#
-#
-#def test_option_get_information_config():
-#    description = "it's ok"
-#    string = 'some informations'
-#    string
-#    i = IntOption('test', description)
-#    od = OptionDescription('od', '', [i])
-#    Config(od)
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    raises(AttributeError, "i.impl_set_information('info', string)")
-##    assert i.impl_get_information('info') == string
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    assert i.impl_get_information('noinfo', 'default') == 'default'
-#    assert i.impl_get_information('doc') == description
-#    assert i.impl_getdoc() == description
-#
-#
-#def test_option_get_information_config2():
-#    description = "it's ok"
-#    string = 'some informations'
-#    i = IntOption('test', description)
-#    i.impl_set_information('info', string)
-#    od = OptionDescription('od', '', [i])
-#    Config(od)
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    raises(AttributeError, "i.impl_set_information('info', 'hello')")
-#    assert i.impl_get_information('info') == string
-#    raises(ValueError, "i.impl_get_information('noinfo')")
-#    assert i.impl_get_information('noinfo', 'default') == 'default'
-#    assert i.impl_get_information('doc') == description
-#    assert i.impl_getdoc() == description
-#
-#
-#def test_optiondescription_get_information():
-#    description = "it's ok"
-#    string = 'some informations'
-#    o = OptionDescription('test', description, [])
-#    o.impl_set_information('info', string)
-#    assert o.impl_get_information('info') == string
-#    raises(ValueError, "o.impl_get_information('noinfo')")
-#    assert o.impl_get_information('noinfo', 'default') == 'default'
-#    assert o.impl_get_information('doc') == description
-#    assert o.impl_getdoc() == description
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    assert i.impl_get_information('noinfo', 'default') == 'default'
+    assert i.impl_get_information('doc') == description
+    assert i.impl_getdoc() == description
+
+
+def test_option_get_information_config2():
+    description = "it's ok"
+    string = 'some informations'
+    i = IntOption('test', description)
+    i.impl_set_information('info', string)
+    od = OptionDescription('od', '', [i])
+    Config(od)
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    raises(AttributeError, "i.impl_set_information('info', 'hello')")
+    assert i.impl_get_information('info') == string
+    raises(ValueError, "i.impl_get_information('noinfo')")
+    assert i.impl_get_information('noinfo', 'default') == 'default'
+    assert i.impl_get_information('doc') == description
+    assert i.impl_getdoc() == description
+
+
+def test_optiondescription_get_information():
+    description = "it's ok"
+    string = 'some informations'
+    o = OptionDescription('test', description, [])
+    o.impl_set_information('info', string)
+    assert o.impl_get_information('info') == string
+    raises(ValueError, "o.impl_get_information('noinfo')")
+    assert o.impl_get_information('noinfo', 'default') == 'default'
+    assert o.impl_get_information('doc') == description
+    assert o.impl_getdoc() == description
 
 
 def test_option_multi():
diff --git a/test/test_parsing_group.py b/test/test_parsing_group.py
index c9288f9..c091aa0 100644
--- a/test/test_parsing_group.py
+++ b/test/test_parsing_group.py
@@ -647,3 +647,19 @@ def test_multi_master_default_slave():
     cfg.ip_admin_eth0.ip_admin_eth0.append('192.168.1.1')
     cfg.cfgimpl_reset_cache()
     assert cfg.ip_admin_eth0.ip_admin_eth0 == ['192.168.1.1']
+
+
+def test_groups_with_master_get_modified_value():
+    ip_admin_eth0 = StrOption('ip_admin_eth0', "ip réseau autorisé", multi=True)
+    netmask_admin_eth0 = StrOption('netmask_admin_eth0', "masque du sous-réseau", multi=True)
+    interface1 = OptionDescription('ip_admin_eth0', '', [ip_admin_eth0, netmask_admin_eth0])
+    interface1.impl_set_group_type(groups.master)
+    maconfig = OptionDescription('toto', '', [interface1])
+    cfg = Config(maconfig)
+    cfg.read_write()
+    assert cfg.cfgimpl_get_values().get_modified_values() == {}
+    cfg.ip_admin_eth0.ip_admin_eth0.append('192.168.1.1')
+    cfg.cfgimpl_reset_cache()
+    assert cfg.cfgimpl_get_values().get_modified_values() == {'ip_admin_eth0.ip_admin_eth0': ('user', ('192.168.1.1',))}
+    cfg.ip_admin_eth0.netmask_admin_eth0 = ['255.255.255.255']
+    assert cfg.cfgimpl_get_values().get_modified_values() == {'ip_admin_eth0.ip_admin_eth0': ('user', ('192.168.1.1',)), 'ip_admin_eth0.netmask_admin_eth0': ({'0': 'user'}, {'0': '255.255.255.255'})}
diff --git a/tiramisu/error.py b/tiramisu/error.py
index ac45751..7407d41 100644
--- a/tiramisu/error.py
+++ b/tiramisu/error.py
@@ -29,6 +29,8 @@ def display_list(lst, separator='and'):
         ret = lst[0]
         if isinstance(ret, unicode):
             ret = ret.encode('utf8')
+        if not isinstance(ret, str):
+            ret = str(ret)
         return ret
     else:
         lst_ = []
@@ -41,6 +43,8 @@ def display_list(lst, separator='and'):
         last = lst[-1]
         if isinstance(last, unicode):
             last = last.encode('utf8')
+        if not isinstance(last, str):
+            last = str(last)
         return ', '.join(lst_) + _(' {} ').format(separator) + last
 
 
diff --git a/tiramisu/storage/dictionary/option.py b/tiramisu/storage/dictionary/option.py
index b0b8c45..716eab0 100644
--- a/tiramisu/storage/dictionary/option.py
+++ b/tiramisu/storage/dictionary/option.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 ""
-# Copyright (C) 2014 Team tiramisu (see AUTHORS for all contributors)
+# Copyright (C) 2014-2017 Team tiramisu (see AUTHORS for all contributors)
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -23,7 +23,7 @@ from ...setting import undefined
 from ...error import ConfigError
 static_tuple = tuple()
 static_set = frozenset()
-if sys.version_info[0] >= 3:  # pragma: optional cover
+if sys.version_info[0] >= 3:  # pragma: no cover
     xrange = range
 
 
@@ -286,7 +286,7 @@ class StorageBase(object):
         self._opt = opt
 
     def _is_string(self, infos):
-        if sys.version_info[0] >= 3:  # pragma: optional cover
+        if sys.version_info[0] >= 3:  # pragma: no cover
             return isinstance(infos, str)
         else:
             return isinstance(infos, str) or isinstance(infos, unicode)
@@ -424,7 +424,7 @@ class StorageOptionDescription(StorageBase):
             raise AttributeError(_('no option {0} found').format(opt))
         return self._cache_paths[1][self._cache_paths[0].index(opt)]
 
-    def impl_get_group_type(self):  # pragma: optional cover
+    def impl_get_group_type(self):
         return self._group_type
 
     def impl_build_cache_option(self, _currpath=None, cache_path=None,
@@ -467,7 +467,7 @@ class StorageOptionDescription(StorageBase):
                 if dynopt == subopt:
                     found = True
                     break
-            if not found:
+            if not found:  # pragma: no cover
                 raise ConfigError(_('cannot find dynpath'))
             subpath = subpath + suffix
             for slength in xrange(length, len(spath)):
@@ -523,7 +523,7 @@ class StorageOptionDescription(StorageBase):
                 return _filter_by_name(path, option)
 
         opts, paths = self._cache_paths
-        for index in range(0, len(paths)):
+        for index in xrange(0, len(paths)):
             option = opts[index]
             if option.impl_is_optiondescription():
                 continue
@@ -556,7 +556,7 @@ class StorageOptionDescription(StorageBase):
     def _getattr(self, name, suffix=undefined, context=undefined, dyn=True):
         error = False
         if suffix is not undefined:
-            if undefined in [suffix, context]:  # pragma: optional cover
+            if undefined in [suffix, context]:  # pragma: no cover
                 raise ConfigError(_("suffix and context needed if "
                                     "it's a dyn option"))
             if name.endswith(suffix):
diff --git a/tiramisu/storage/dictionary/value.py b/tiramisu/storage/dictionary/value.py
index 64fa42d..0dc82bc 100644
--- a/tiramisu/storage/dictionary/value.py
+++ b/tiramisu/storage/dictionary/value.py
@@ -35,9 +35,6 @@ class Values(Cache):
     def getsession(self):
         pass
 
-    def delsession(self, session):
-        pass
-
     def _setvalue_info(self, nb, idx, value, values, index, vidx):
         lst = list(self._values[nb])
         if idx is None:
@@ -82,8 +79,6 @@ class Values(Cache):
         if isinstance(value, list):
             value = tuple(value)
         vidx = self._setvalue_info(2, idx, value, values, index, vidx)
-        if isinstance(value, list):
-            value = tuple(value)
         self._setvalue_info(3, idx, owner, values, index, vidx)
         self._values = tuple(values)
 
@@ -183,32 +178,20 @@ class Values(Cache):
         _values == ((path1, path2), ((idx1_1, idx1_2), None), ((value1_1, value1_2), value2), ((owner1_1, owner1_2), owner2))
         """
         if path in self._values[0]:
-            idx = self._values[0].index(path)
-            if isinstance(self._values[1][idx], tuple):
-                if index is None:
-                    raise ValueError('index is mandatory')
-            elif index is not None:
-                raise ValueError('index is forbidden')
-
-            if self._values[1][idx] is None:
-                if index is None:
-                    value = self._values[nb][idx]
-                else:
-                    value = self._values[nb][idx][index]
+            path_idx = self._values[0].index(path)
+            indexes = self._values[1][path_idx]
+            if indexes is None:
+                if index is not None:  # pragma: no cover
+                    raise ValueError('index is forbidden')
+                value = self._values[nb][path_idx]
             else:
-                if index is not None:
-                    if index in self._values[1][idx]:
-                        subidx = self._values[1][idx].index(index)
-                        value = self._values[nb][idx][subidx]
-                    else:
-                        value = undefined
+                if index is None:  # pragma: no cover
+                    raise ValueError('index is mandatory')
+                if index in indexes:
+                    subidx = indexes.index(index)
+                    value = self._values[nb][path_idx][subidx]
                 else:
-                    value = []
-                    for i in xrange(0, max(self._values[1][idx])):
-                        if i in self._values[1][idx]:
-                            value.append(self._values[nb][idx][self._values[1][idx].index(i)])
-                        else:
-                            value.append(undefined)
+                    value = undefined
         else:
             value = undefined
         if isinstance(value, tuple):
diff --git a/tiramisu/storage/util.py b/tiramisu/storage/util.py
index 9948de8..064d0a1 100644
--- a/tiramisu/storage/util.py
+++ b/tiramisu/storage/util.py
@@ -19,7 +19,7 @@ from ..setting import owners
 
 
 class SerializeObject(object):
-    def __getstate__(self):
+    def __getstate__(self):  # pragma: no cover
         ret = {}
         for key in dir(self):
             if not key.startswith('__'):
@@ -53,7 +53,7 @@ class Cache(object):
                     str_owner = []
                     _value.append(value[2])
                     for owner in value[3]:
-                        if isinstance(owner, list):
+                        if isinstance(owner, list):  # pragma: no cover
                             str_owners = []
                             for subowner in owner:
                                 str_owners.append(str(subowner))
@@ -64,7 +64,7 @@ class Cache(object):
                     states[slot] = _value
                 else:
                     states[slot] = value
-            except AttributeError:
+            except AttributeError:  # pragma: no cover
                 pass
         return states
 
@@ -72,7 +72,7 @@ class Cache(object):
         def convert_owner(owner):
             try:
                 owner = getattr(owners, owner)
-            except AttributeError:
+            except AttributeError:  # pragma: no cover
                 owners.addowner(owner)
                 owner = getattr(owners, owner)
             return owner
@@ -86,7 +86,7 @@ class Cache(object):
                 _value.append(value[2])
                 obj_owner = []
                 for owner in value[3]:
-                    if isinstance(owner, list):
+                    if isinstance(owner, list):  # pragma: no cover
                         obj_owners = []
                         for subowner in owner:
                             obj_owners.append(convert_owner(subowner))
@@ -104,7 +104,7 @@ class Cache(object):
         value, created = self._cache[path][index]
         if created is None or exp <= created:
             return True, value
-        return False, None
+        return False, None  # pragma: no cover
 
     def hascache(self, path, index):
         """ path is in the cache