ex 6.4

stock.py

@@ -2,8 +2,7 @@ from structure import Structure
 
 
 class Stock(Structure):
-    def __init__(self, name, shares, price):
-        self._init()
+    _fields = ('name', 'shares', 'price')
 
     @property
     def cost(self):
@@ -12,5 +11,4 @@ class Stock(Structure):
     def sell(self, nshares):
         self.shares -= nshares
 
-
-Stock.set_fields()
+Stock.create_init()

structure.py

@@ -5,13 +5,6 @@ import sys
 class Structure:
     _fields = ()
 
-    @staticmethod
-    def _init():
-        locs = sys._getframe(1).f_locals
-        self = locs.pop('self')
-        for name, val in locs.items():
-            setattr(self, name, val)
-
     def __repr__(self):
         args = map(lambda field: f"{field}={getattr(self, field)!r}", self._fields)
         return f"{type(self).__name__}({', '.join(args)})"
@@ -23,6 +16,10 @@ class Structure:
             raise AttributeError(f"No attribute {name}")
 
     @classmethod
-    def set_fields(cls):
-        sig = inspect.signature(cls)
-        cls._fields = tuple(sig.parameters)
+    def create_init(cls):
+        code = f'def __init__(self, {", ".join(cls._fields)}):\n'
+        for name in cls._fields:
+            code += f'    self.{name} = {name}\n'
+        locs = {}
+        exec(code, locs)
+        cls.__init__ = locs['__init__']