80 lines
2.1 KiB
Python
80 lines
2.1 KiB
Python
"""
|
|
|
|
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)[:3]
|
|
['_NonBlank#description', '_Quantity#price', '_Quantity#weight']
|
|
>>> LineItem.description.storage_name
|
|
'_NonBlank#description'
|
|
>>> raisins.description
|
|
'Golden raisins'
|
|
>>> getattr(raisins, '_NonBlank#description')
|
|
'Golden raisins'
|
|
|
|
If the descriptor is accessed in the class, the descriptor object is
|
|
returned:
|
|
|
|
>>> LineItem.weight # doctest: +ELLIPSIS
|
|
<model_v7.Quantity object at 0x...>
|
|
>>> LineItem.weight.storage_name
|
|
'_Quantity#weight'
|
|
|
|
|
|
The `NonBlank` descriptor prevents empty or blank strings to be used
|
|
for the description:
|
|
|
|
>>> br_nuts = LineItem('Brazil Nuts', 10, 34.95)
|
|
>>> br_nuts.description = ' '
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: value cannot be empty or blank
|
|
>>> void = LineItem('', 1, 1)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: value cannot be empty or blank
|
|
|
|
"""
|
|
|
|
# tag::LINEITEM_V7[]
|
|
import model_v7 as model
|
|
|
|
class LineItem(model.Entity): # <1>
|
|
description = model.NonBlank()
|
|
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_V7[]
|