diff --git a/src/8/extending_classes_with_mixins/example2.py b/src/8/extending_classes_with_mixins/example2.py
index fb3c931..cf1febc 100644
--- a/src/8/extending_classes_with_mixins/example2.py
+++ b/src/8/extending_classes_with_mixins/example2.py
@@ -1,23 +1,33 @@
 class RestrictKeysMixin:
-    def __init__(self, *args, _restrict_key_type, **kwargs):
+    # there is an underscore not present which is added in it 
+    def __init__(self, _restrict_key_type, *args, **kwargs):
         self.__restrict_key_type = _restrict_key_type
         super().__init__(*args, **kwargs)
     
     def __setitem__(self, key, value):
         if not isinstance(key, self.__restrict_key_type):
-            raise TypeError('Keys must be ' + str(self.__restrict_key_type))
+            raise TypeError(f'Keys must be of type {self.__restrict_key_type.__name__}')
         super().__setitem__(key, value)
 
 # Example
 
 class RDict(RestrictKeysMixin, dict):
-    pass
- 
-d = RDict(_restrict_key_type=str)
-e = RDict([('name','Dave'), ('n',37)], _restrict_key_type=str)
+    def __init__(self, *args, _restrict_key_type=None, **kwargs):
+        if _restrict_key_type is None:
+            raise ValueError("_restrict_key_type must be specified")
+        super().__init__(_restrict_key_type=_restrict_key_type, *args, **kwargs)
+
+# Usage
+try:
+    d = RDict()  # This will raise a ValueError because _restrict_key_type is not specified
+except ValueError as e:
+    print(e)
+
+e = RDict([('name', 'Dave'), ('n', 37)], _restrict_key_type=str)
 f = RDict(name='Dave', n=37, _restrict_key_type=str)
 print(f)
+
 try:
-    f[42] = 10
+    f[42] = 10  # This will raise a TypeError because the key is not of type str
 except TypeError as e:
     print(e)