updated from Atlas

19-dyn-attr-prop/bulkfood/bulkfood_v2prop.py

@@ -0,0 +1,69 @@
+"""
+
+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 value of the attributes managed by the properties are stored in
+instance attributes, created in each ``LineItem`` instance::
+
+# BEGIN LINEITEM_V2_PROP_DEMO
+    >>> nutmeg = LineItem('Moluccan nutmeg', 8, 13.95)
+    >>> nutmeg.weight, nutmeg.price  # <1>
+    (8, 13.95)
+    >>> sorted(vars(nutmeg).items())  # <2>
+    [('description', 'Moluccan nutmeg'), ('price', 13.95), ('weight', 8)]
+
+# END LINEITEM_V2_PROP_DEMO
+
+"""
+
+
+# BEGIN LINEITEM_V2_PROP_FACTORY_FUNCTION
+def quantity(storage_name):  # <1>
+
+    def qty_getter(instance):  # <2>
+        return instance.__dict__[storage_name]  # <3>
+
+    def qty_setter(instance, value):  # <4>
+        if value > 0:
+            instance.__dict__[storage_name] = value  # <5>
+        else:
+            raise ValueError('value must be > 0')
+
+    return property(qty_getter, qty_setter)  # <6>
+# END LINEITEM_V2_PROP_FACTORY_FUNCTION
+
+
+# BEGIN LINEITEM_V2_PROP_CLASS
+class LineItem:
+    weight = quantity('weight')  # <1>
+    price = quantity('price')  # <2>
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight  # <3>
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price  # <4>
+# END LINEITEM_V2_PROP_CLASS