diff --git a/tests/test_readme.py b/tests/test_readme.py
index b74de2d..65089ee 100644
--- a/tests/test_readme.py
+++ b/tests/test_readme.py
@@ -487,13 +487,13 @@ prog.py: error: unrecognized arguments: --int
 
 def test_readme_cross_tree(json):
     output = """usage: prog.py "none" [-h] [-v] [-nv] {str,list,int,none}
-prog.py: error: unrecognized arguments: --int
+prog.py: error: unrecognized arguments: --root.int
 """
     parser = TiramisuCmdlineParser(get_config(json, True), 'prog.py')
     f = StringIO()
     with redirect_stderr(f):
         try:
-            parser.parse_args(['none', '--int'])
+            parser.parse_args(['none', '--root.int'])
         except SystemExit as err:
             assert str(err) == "2"
         else:
@@ -503,13 +503,13 @@ prog.py: error: unrecognized arguments: --int
 
 def test_readme_cross_tree_remove(json):
     output = """usage: prog.py "none" [-h] [-v] [-nv]
-prog.py: error: unrecognized arguments: --int
+prog.py: error: unrecognized arguments: --root.int
 """
     parser = TiramisuCmdlineParser(get_config(json, True), 'prog.py', display_modified_value=False)
     f = StringIO()
     with redirect_stderr(f):
         try:
-            parser.parse_args(['none', '--int'])
+            parser.parse_args(['none', '--root.int'])
         except SystemExit as err:
             assert str(err) == "2"
         else:
@@ -859,3 +859,32 @@ def test_readme_longargument(json):
     parser = TiramisuCmdlineParser(config, 'prog.py')
     parser.parse_args(['list', '--list', 'a', '--v'])
     assert config.value.dict() == output
+
+
+def test_readme_unknown_key(json):
+    output1 = """usage: prog.py [-h] [-v] [-nv] {str,list,int,none}
+prog.py: error: unrecognized arguments: --unknown
+"""
+    output2 = """usage: prog.py [-h] [-v] [-nv] {str,list,int,none}
+prog.py: error: unrecognized arguments: --root.unknown
+"""
+    parser = TiramisuCmdlineParser(get_config(json, True), 'prog.py', fullpath=False)
+    f = StringIO()
+    with redirect_stderr(f):
+        try:
+            parser.parse_args(['--unknown'])
+        except SystemExit as err:
+            assert str(err) == "2"
+        else:
+            raise Exception('must raises')
+    assert f.getvalue() == output1
+
+    f = StringIO()
+    with redirect_stderr(f):
+        try:
+            parser.parse_args(['--root.unknown'])
+        except SystemExit as err:
+            assert str(err) == "2"
+        else:
+            raise Exception('must raises')
+    assert f.getvalue() == output2
diff --git a/tiramisu_cmdline_parser/__init__.py b/tiramisu_cmdline_parser/__init__.py
index 124abc5..2a5a6ac 100644
--- a/tiramisu_cmdline_parser/__init__.py
+++ b/tiramisu_cmdline_parser/__init__.py
@@ -1,4 +1,4 @@
 from .api import TiramisuCmdlineParser
 
-__version__ = "0.2"
+__version__ = "0.3"
 __all__ = ('TiramisuCmdlineParser',)
diff --git a/tiramisu_cmdline_parser/api.py b/tiramisu_cmdline_parser/api.py
index 191da78..17cf642 100644
--- a/tiramisu_cmdline_parser/api.py
+++ b/tiramisu_cmdline_parser/api.py
@@ -20,7 +20,7 @@ from gettext import gettext as _
 try:
     from tiramisu import Config
     from tiramisu.error import PropertiesOptionError, RequirementError, LeadershipError
-except (ModuleNotFoundError, ImportError):
+except ImportError:
     Config = None
     from tiramisu_api.error import PropertiesOptionError
     RequirementError = PropertiesOptionError
@@ -29,7 +29,7 @@ try:
     from tiramisu__api import Config as ConfigJson
     if Config is None:
         Config = ConfigJson
-except ModuleNotFoundError:
+except ImportError:
     ConfigJson = Config
 
 
@@ -44,7 +44,7 @@ def get_choice_list(obj, properties, display):
     if display:
         choices = '{{{}}}'.format(','.join(choices))
         if 'mandatory' not in properties:
-            choices = f'[{choices}]'
+            choices = '[{}]'.format(choices)
     return choices
 
 
@@ -376,9 +376,9 @@ class TiramisuCmdlineParser(ArgumentParser):
         if type != 'boolean':
             if isinstance(value, list):
                 for val in value:
-                    self.prog += f' "{val}"'
+                    self.prog += ' "{}"'.format(val)
             else:
-                self.prog += f' "{value}"'
+                self.prog += ' "{}"'.format(value)
 
     def _config_list(self,
                      config: Config,
@@ -512,7 +512,7 @@ class TiramisuCmdlineParser(ArgumentParser):
                     else:
                         kwargs['nargs'] = 2
                         if _forhelp and 'mandatory' not in properties:
-                            metavar = f'[{metavar}]'
+                            metavar = '[{}]'.format(metavar)
                     if option.type() == 'choice':
                         # do not manage choice with argparse there is problem with integer problem
                         kwargs['metavar'] = ('INDEX', get_choice_list(obj, properties, True))