ex 4.3

descrip.py

@@ -0,0 +1,12 @@
+class Descriptor:
+    def __init__(self, name):
+        self.name = name
+
+    def __get__(self, instance, cls):
+        print(f"{self.name}:__get__")
+
+    def __set__(self, instance, value):
+        print(f"{self.name}:__set__ {value}")
+
+    def __delete__(self, instance):
+        print(f"{self.name}:__delete__")

validate.py

@@ -1,8 +1,17 @@
 class Validator:
+    def __init__(self, name=None):
+        self.name = name
+
     @classmethod
     def check(cls, value):
         return value
 
+    def __set__(self, instance, value):
+        instance.__dict__[self.name] = self.check(value)
+
+    def __set_name__(self, cls, name):
+        self.name = name
+
 
 class Typed(Validator):
     expected_type = object
@@ -55,8 +64,9 @@ class NonEmptyString(String, NonEmpty):
 
 
 class Stock:
-    _types = (str, int, float)
-    __slots__ = ["name", "_shares", "_price"]
+    name = String()
+    shares = PositiveInteger()
+    price = PositiveFloat()
 
     def __init__(self, name, shares, price):
         self.name = name
@@ -77,31 +87,12 @@ class Stock:
 
     @classmethod
     def from_row(cls, row):
-        values = [func(val) for func, val in zip(cls._types, row)]
-        return cls(*values)
+        return cls(*row)
 
     @property
     def cost(self):
         return self.shares * self.price
 
-    @property
-    def shares(self):
-        return self._shares
-
-    @shares.setter
-    def shares(self, value):
-        PositiveInteger.check(value)
-        self._shares = value
-
-    @property
-    def price(self):
-        return self._price
-
-    @price.setter
-    def price(self, value):
-        PositiveFloat.check(value)
-        self._price = value
-
     def sell(self, num):
         self.shares -= num
         if self.shares < 0: