Update page 'Day 5 homework'

Day 5 homework.md

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+**The assignment for tonight is to write a class named Vault containing an attribute named "treasure" which returns "gold" under normal circumstances, but a warning message such as "attribute deleted!" if it detects any of its attributes have been changed.  You can use the descriptor protocol (__set__, etc) to detect if its attributes have been changed, and it will have to check its own __dict__ against a known good copy before accessing the treasure attribute to make sure that the attributes are what they're supposed to be.**
+
+```
+class Vault:
+    def __init__(self):
+        self._treasure = "gold"
+        self._attributes = dict(self.__dict__)
+        
+    def __setattr__(self, name, value):
+        if name != "_attributes" and name not in self._attributes:
+            print("attribute deleted!")
+        self._attributes[name] = value
+        super().__setattr__("_attributes", dict(self.__dict__))
+        
+    @property
+    def treasure(self):
+        if self.__dict__ != self._attributes:
+            print("attribute deleted!")
+        return self._treasure
+```
+In this implementation, the __init__ method initializes the Vault instance with a treasure attribute set to "gold", as well as a _attributes attribute that is a copy of the instance's __dict__.
+
+The __setattr__ method is overridden to check whether a new attribute is being added to the instance, and if so, whether the attribute already existed in the _attributes dictionary. If the attribute did not exist in _attributes, it means that it has been added to the instance after initialization, and so a warning message is printed. The _attributes dictionary is then updated with the new attribute, and a new copy of the instance's __dict__ is stored in the _attributes attribute.
+
+Finally, the treasure property is defined to return the value of the _treasure attribute, but only if the instance's __dict__ matches the _attributes dictionary. If any attributes have been added or deleted since initialization, a warning message is printed instead.
+