ex 6.3

stock.py

@@ -2,8 +2,6 @@ from structure import Structure
 
 
 class Stock(Structure):
-    _fields = ('name', 'shares', 'price')
-
     def __init__(self, name, shares, price):
         self._init()
 
@@ -13,3 +11,6 @@ class Stock(Structure):
 
     def sell(self, nshares):
         self.shares -= nshares
+
+
+Stock.set_fields()

structure.py

@@ -1,3 +1,4 @@
+import inspect
 import sys
 
 
@@ -20,3 +21,8 @@ class Structure:
             super().__setattr__(name, value)
         else:
             raise AttributeError(f"No attribute {name}")
+
+    @classmethod
+    def set_fields(cls):
+        sig = inspect.signature(cls)
+        cls._fields = tuple(sig.parameters)