update from Atlas

descriptors/bulkfood_v5.py

@@ -0,0 +1,75 @@
+"""
+
+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 descriptors are stored in
+alternate attributes, created by the descriptors in each ``LineItem``
+instance::
+
+    >>> raisins = LineItem('Golden raisins', 10, 6.95)
+    >>> dir(raisins)  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
+    ['_NonBlank_0', '_Quantity_0', '_Quantity_1', '__class__', ...
+     'description', 'price', 'subtotal', 'weight']
+    >>> raisins._Quantity_0
+    10
+    >>> raisins._Quantity_1
+    6.95
+
+If the descriptor is accessed in the class, the descriptor object is
+returned:
+
+    >>> LineItem.price  # doctest: +ELLIPSIS
+    <model_v5.Quantity object at 0x...>
+    >>> br_nuts = LineItem('Brazil nuts', 10, 34.95)
+    >>> br_nuts.price
+    34.95
+
+The `NonBlank` descriptor prevents empty or blank strings to be used
+for the description:
+
+    >>> br_nuts.description = ' '
+    Traceback (most recent call last):
+        ...
+    ValueError: value cannot be empty or blank
+
+
+"""
+
+# BEGIN LINEITEM_V5
+import model_v5 as model  # <1>
+
+
+class LineItem:
+    description = model.NonBlank()  # <2>
+    weight = model.Quantity()
+    price = model.Quantity()
+
+    def __init__(self, description, weight, price):
+        self.description = description
+        self.weight = weight
+        self.price = price
+
+    def subtotal(self):
+        return self.weight * self.price
+# END LINEITEM_V5