Update page 'Day 5&6 Homework - Karen'

Day 5 Homework - Karen.md

@@ -1,30 +0,0 @@
-**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._original_dict = dict(self.__dict__)
-
-    def __setattr__(self, name, value):
-        if name != "_treasure" and name in self.__dict__ and self._original_dict.get(name) != value:
-            print("attribute deleted!")
-        self.__dict__[name] = value
-
-    @property
-    def treasure(self):
-        if self.__dict__ != self._original_dict:
-            print("attribute deleted!")
-        return self._treasure
-v = Vault()
-print(v.treasure)
-```
-To assess other's Vault (although it may not be ethical), we can use `__getattribute__` method like:
-
-```
-class EvilVault(Vault):
-    def __getattribute__(self, name):
-        if name == "treasure":
-            return "gold"
-        return super().__getattribute__(name)
-```

Day 5&6 Homework - Karen.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._original_dict = dict(self.__dict__)
+
+    def __setattr__(self, name, value):
+        if name != "_treasure" and name in self.__dict__ and self._original_dict.get(name) != value:
+            print("attribute deleted!")
+        self.__dict__[name] = value
+
+    @property
+    def treasure(self):
+        if self.__dict__ != self._original_dict:
+            print("attribute deleted!")
+        return self._treasure
+v = Vault()
+print(v.treasure)
+```
+
+Here is another method using `__getattribute__` and `__setattr__`.
+
+```
+class Vault:
+    def __init__(self):
+        self._treasure = "gold"
+        self._known_good_copy = self.__dict__.copy()
+
+    def __getattribute__(self, name):
+        if name == "treasure":
+            if self.__dict__ != self._known_good_copy:
+                print("Attribute deleted!")
+            return self._treasure
+        else:
+            return object.__getattribute__(self, name)
+
+    def __setattr__(self, name, value):
+        if name != "_treasure" and name != "_known_good_copy":
+            print("Attribute deletion detected!")
+            self._known_good_copy = self.__dict__.copy()
+        object.__setattr__(self, name, value)
+v = Vault()
+print(v.treasure)
+```
+
+Also, we can define a descriptor by implementing the `__get__`, `__set__`, and `__delete__` methods.
+
+```
+class Vault:
+    def __init__(self):
+        self._treasure = "gold"
+        self._known_good_copy = self.__dict__.copy()
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+        else:
+            if instance.__dict__ != self._known_good_copy:
+                print("Attribute deleted!")
+            return self._treasure
+
+    def __set__(self, instance, value):
+        print("Attribute deletion detected!")
+        self._known_good_copy = instance.__dict__.copy()
+
+    def __delete__(self, instance):
+        print("Attribute deletion detected!")
+        self._known_good_copy = instance.__dict__.copy()
+
+    def __set_name__(self, owner, name):
+        self.name = name
+v = Vault()
+print(v._treasure)
+```
+
+Unfortunately, I didn't figure out what happened to the code that I used `super().__setattr__` last week, so I create a question on stack overflow to see if someone can help me with this issue.
+https://stackoverflow.com/questions/75990535/attributeerror-and-recursionerror-happened-when-using-setattr-in-python
+
+```
+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
+
+v = Vault()
+print(v.treasure)
+```
+
+To assess other's Vault (although it may not be ethical), we can use `__getattribute__` method like:
+
+```
+class EvilVault(Vault):
+    def __getattribute__(self, name):
+        if name == "treasure":
+            return "gold"
+        return super().__getattribute__(name)
+```
+Or I think we can use another easier way as accessing the attribute through the class's dictionary:
+
+```
+Vault.__dict__["_treasure"]
+```