ex6.1

stock.py

@@ -1,67 +1,12 @@
-class Stock:
-    _types = (str, int, float)
-    __slots__ = ["name", "_shares", "_price"]
+from structure import Structure
 
-    def __init__(self, name, shares, price):
-        self.name = name
-        self.shares = shares
-        self.price = price
 
-    def __repr__(self):
-        return f"Stock({self.name!r}, {self.shares!r}, {self.price!r})"
-
-    def __eq__(self, other):
-        if not isinstance(other, Stock):
-            return False
-        return (self.name, self.shares, self.price) == (
-            other.name,
-            other.shares,
-            other.price,
-        )
-
-    @classmethod
-    def from_row(cls, row):
-        values = [func(val) for func, val in zip(cls._types, row)]
-        return cls(*values)
+class Stock(Structure):
+    _fields = ('name', 'shares', 'price')
 
     @property
     def cost(self):
         return self.shares * self.price
 
-    @property
-    def shares(self):
-        return self._shares
-
-    @shares.setter
-    def shares(self, value):
-        if not isinstance(value, self._types[1]):
-            raise TypeError("Expected int")
-        if value < 0:
-            raise ValueError("Expected positive integer")
-        self._shares = value
-
-    @property
-    def price(self):
-        return self._price
-
-    @price.setter
-    def price(self, value):
-        if not isinstance(value, self._types[2]):
-            raise TypeError("Expected float")
-        if value < 0.0:
-            raise ValueError("Expected positive float")
-        self._price = value
-
-    def sell(self, num):
-        self.shares -= num
-        if self.shares < 0:
-            self.shares = 0
-
-
-def print_portfolio(portfolio):
-    headers = ("name", "shares", "price")
-    fmtstr = "{0: >10} {1: >10} {2: >10}"
-    print(fmtstr.format(*headers))
-    print("{0:->10} {1:->10} {2:->10}".format("", "", ""))
-    for stock in portfolio:
-        print(fmtstr.format(stock.name, stock.shares, stock.price))
+    def sell(self, nshares):
+        self.shares -= nshares

structure.py

@@ -0,0 +1,18 @@
+class Structure:
+    _fields = ()
+
+    def __init__(self, *args):
+        if len(args) != len(self._fields):
+            raise TypeError(f'Expected {len(self._fields)} arguments')
+        for pos, field in enumerate(self._fields):
+            setattr(self, field, args[pos])
+
+    def __repr__(self):
+        args = map(lambda field: f"{field}={getattr(self, field)!r}", self._fields)
+        return f"{type(self).__name__}({', '.join(args)})"
+
+    def __setattr__(self, name, value):
+        if name in self._fields or name[0] == '_':
+            super().__setattr__(name, value)
+        else:
+            raise AttributeError(f"No attribute {name}")