61 lines
1.4 KiB
Plaintext
61 lines
1.4 KiB
Plaintext
"""
|
|
WARNING: Broken implementation for demonstration purposes.
|
|
|
|
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
|
|
|
|
Negative or 0 price is not acceptable either::
|
|
|
|
>>> truffle = LineItem('White truffle', 100, 0)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: value must be > 0
|
|
|
|
|
|
No change was made::
|
|
|
|
>>> raisins.weight
|
|
10
|
|
|
|
"""
|
|
|
|
|
|
class Quantity:
|
|
|
|
def __init__(self, storage_name):
|
|
self.storage_name = storage_name
|
|
|
|
def __set__(self, instance, value):
|
|
if value > 0:
|
|
instance.__dict__[self.storage_name] = value
|
|
else:
|
|
raise ValueError('value must be > 0')
|
|
|
|
|
|
class LineItem:
|
|
weight = Quantity('weight')
|
|
price = Quantity('weight') # <-- this is the bug discussed in the book
|
|
|
|
def __init__(self, description, weight, price):
|
|
self.description = description
|
|
self.weight = weight
|
|
self.price = price
|
|
|
|
def subtotal(self):
|
|
return self.weight * self.price
|