1 files changed, 36 insertions, 1 deletions
diff --git a/python/vyos/utils/dict.py b/python/vyos/utils/dict.py
index 66fe6dad3..9484eacdd 100644
--- a/python/vyos/utils/dict.py
+++ b/python/vyos/utils/dict.py
@@ -13,7 +13,6 @@
 # You should have received a copy of the GNU Lesser General Public
 # License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 
-
 def colon_separated_to_dict(data_string, uniquekeys=False):
     """ Converts a string containing newline-separated entries
         of colon-separated key-value pairs into a dict.
@@ -270,3 +269,39 @@ def check_mutually_exclusive_options(d, keys, required=False):
 
     if required and (len(present_keys) < 1):
         raise ValueError(f"At least one of the following options is required: {orig_keys}")
+
+class FixedDict(dict):
+    """
+    FixedDict: A dictionnary not allowing new keys to be created after initialisation.
+
+    >>> f = FixedDict(**{'count':1})
+    >>> f['count'] = 2
+    >>> f['king'] = 3
+      File "...", line ..., in __setitem__
+    raise ConfigError(f'Option "{k}" has no defined default')
+    """
+
+    from vyos import ConfigError
+
+    def __init__(self, **options):
+        self._allowed = options.keys()
+        super().__init__(**options)
+
+    def __setitem__(self, k, v):
+        """
+        __setitem__ is a builtin which is called by python when setting dict values:
+        >>> d = dict()
+        >>> d['key'] = 'value'
+        >>> d
+        {'key': 'value'}
+
+        is syntaxic sugar for
+
+        >>> d = dict()
+        >>> d.__setitem__('key','value')
+        >>> d
+        {'key': 'value'}
+        """
+        if k not in self._allowed:
+            raise ConfigError(f'Option "{k}" has no defined default')
+        super().__setitem__(k, v)