ex 7.3

stock.py

@@ -1,14 +1,21 @@
 from structure import Structure
+from validate import PositiveFloat, PositiveInteger, String
 
 
 class Stock(Structure):
-    _fields = ('name', 'shares', 'price')
+    _types = ()
+    name = String()
+    shares = PositiveInteger()
+    price = PositiveFloat()
 
     @property
     def cost(self):
         return self.shares * self.price
 
-    def sell(self, nshares):
+    def sell(self, nshares: PositiveInteger):
         self.shares -= nshares
 
-Stock.create_init()
+    @classmethod
+    def from_row(cls, row):
+        rowdata = [func(val) for func, val in zip(cls._types, row)]
+        return cls(*rowdata)

structure.py

@@ -1,10 +1,26 @@
-import inspect
-import sys
+from validate import Validator, validated
+
+
+def validate_attributes(cls):
+    validators = []
+    for name, val in vars(cls).items():
+        if isinstance(val, Validator):
+            validators.append(val)
+        elif callable(val) and val.__annotations__:
+            setattr(cls, name, validated(val))
+    cls._fields = tuple(val.name for val in validators)
+    cls._types = tuple(getattr(v, 'expected_type', lambda x: x) for v in validators)
+    if cls._fields:
+        cls.create_init()
+    return cls
 
 
 class Structure:
     _fields = ()
 
+    def __init_subclass__(cls):
+        validate_attributes(cls)
+
     def __repr__(self):
         args = map(lambda field: f"{field}={getattr(self, field)!r}", self._fields)
         return f"{type(self).__name__}({', '.join(args)})"