added chapter map to README

22-dyn-attr-prop/bulkfood/bulkfood_v2.py

@@ -0,0 +1,63 @@
+"""
+
+A line item for a bulk food order has description, weight and price fields::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> raisins.weight, raisins.description, raisins.price
+    (10, 'Golden raisins', 6.95)
+
+A ``subtotal`` method gives the total price for that line item::
+
+    >>> raisins.subtotal()
+    69.5
+
+The weight of a ``LineItem`` must be greater than 0::
+
+    >>> raisins.weight = -20
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+No change was made::
+
+    >>> raisins.weight
+    10
+
+The check is also performed on instantiation::
+
+    >>> walnuts = LineItem('walnuts', 0, 10.00)
+    Traceback (most recent call last):
+        ...
+    ValueError: value must be > 0
+
+The proteced attribute can still be accessed if needed for some reason, such as
+white box testing)::
+
+    >>> raisins._LineItem__weight
+    10
+
+"""
+
+
+# BEGIN LINEITEM_V2
+class LineItem:
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight  # <1>
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+
+    @property  # <2>
+    def weight(self):  # <3>
+        return self.__weight  # <4>
+
+    @weight.setter  # <5>
+    def weight(self, value):
+        if value > 0:
+            self.__weight = value  # <6>
+        else:
+            raise ValueError('value must be > 0')  # <7>
+# END LINEITEM_V2