diff --git a/tiramisu/option.py b/tiramisu/option.py
index d82e771..9937a6e 100644
--- a/tiramisu/option.py
+++ b/tiramisu/option.py
@@ -346,7 +346,7 @@ class Option(BaseInformation):
             raise ValueError('cannot add consistency with itself')
         if self.impl_is_multi() != opt.impl_is_multi():
             raise ValueError('options in consistency should be multi in two sides')
-        func = '_cons_{}'.format(func)
+        func = '_cons_{0}'.format(func)
         self._launch_consistency(func, self, self.impl_getdefault(), None, None, opt)
         self._consistencies.append((func, opt))
         self.impl_validate(self.impl_getdefault())
@@ -519,7 +519,7 @@ class NetmaskOption(Option):
 
     def _validate(self, value):
         try:
-            IP('0.0.0.0/{}'.format(value))
+            IP('0.0.0.0/{0}'.format(value))
             return True
         except ValueError:
             return False
@@ -665,7 +665,7 @@ class OptionDescription(BaseInformation):
         try:
             return self._children[1][self._children[0].index(name)]
         except ValueError:
-            raise AttributeError(_('unknown Option {} in OptionDescription {}'
+            raise AttributeError(_('unknown Option {0} in OptionDescription {1}'
                                  '').format(name, self._name))
 
     def impl_getkey(self, config):
@@ -739,13 +739,13 @@ class OptionDescription(BaseInformation):
         try:
             return self._cache_paths[0][self._cache_paths[1].index(path)]
         except ValueError:
-            raise AttributeError(_('no option for path {}').format(path))
+            raise AttributeError(_('no option for path {0}').format(path))
 
     def impl_get_path_by_opt(self, opt):
         try:
             return self._cache_paths[1][self._cache_paths[0].index(opt)]
         except ValueError:
-            raise AttributeError(_('no option {} found').format(opt))
+            raise AttributeError(_('no option {0} found').format(opt))
 
     # ____________________________________________________________
     def impl_set_group_type(self, group_type):
@@ -756,7 +756,7 @@ class OptionDescription(BaseInformation):
         """
         if self._group_type != groups.default:
             raise TypeError(_('cannot change group_type if already set '
-                            '(old {}, new {})').format(self._group_type, group_type))
+                            '(old {0}, new {1})').format(self._group_type, group_type))
         if isinstance(group_type, groups.GroupType):
             self._group_type = group_type
             if isinstance(group_type, groups.MasterGroupType):
@@ -767,10 +767,10 @@ class OptionDescription(BaseInformation):
                 master = None
                 for child in self.impl_getchildren():
                     if isinstance(child, OptionDescription):
-                        raise ValueError(_("master group {} shall not have "
+                        raise ValueError(_("master group {0} shall not have "
                                          "a subgroup").format(self._name))
                     if isinstance(child, SymLinkOption):
-                        raise ValueError(_("master group {} shall not have "
+                        raise ValueError(_("master group {0} shall not have "
                                          "a symlinkoption").format(self._name))
                     if not child.impl_is_multi():
                         raise ValueError(_("not allowed option {0} in group {1}"
@@ -783,7 +783,7 @@ class OptionDescription(BaseInformation):
                     else:
                         slaves.append(child)
                 if master is None:
-                    raise ValueError(_('master group with wrong master name for {}'
+                    raise ValueError(_('master group with wrong master name for {0}'
                                      '').format(self._name))
                 master._master_slaves = tuple(slaves)
                 for child in self.impl_getchildren():
@@ -791,7 +791,7 @@ class OptionDescription(BaseInformation):
                         child._master_slaves = master
                         child._multitype = multitypes.slave
                 if not identical_master_child_name:
-                    raise ValueError(_("the master group: {} has not any "
+                    raise ValueError(_("the master group: {0} has not any "
                                      "master child").format(self._name))
         else:
             raise ValueError(_('not allowed group_type : {0}').format(group_type))