70 lines
1.8 KiB
Python
70 lines
1.8 KiB
Python
"""
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A line item for a bulk food order has description, weight and price fields::
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>>> raisins = LineItem('Golden raisins', 10, 6.95)
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>>> raisins.weight, raisins.description, raisins.price
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(10, 'Golden raisins', 6.95)
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A ``subtotal`` method gives the total price for that line item::
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>>> raisins.subtotal()
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69.5
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The weight of a ``LineItem`` must be greater than 0::
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>>> raisins.weight = -20
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Traceback (most recent call last):
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...
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ValueError: value must be > 0
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No change was made::
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>>> raisins.weight
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10
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The value of the attributes managed by the properties are stored in
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instance attributes, created in each ``LineItem`` instance::
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# tag::LINEITEM_V2_PROP_DEMO[]
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>>> nutmeg = LineItem('Moluccan nutmeg', 8, 13.95)
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>>> nutmeg.weight, nutmeg.price # <1>
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(8, 13.95)
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>>> sorted(vars(nutmeg).items()) # <2>
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[('description', 'Moluccan nutmeg'), ('price', 13.95), ('weight', 8)]
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# end::LINEITEM_V2_PROP_DEMO[]
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"""
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# tag::LINEITEM_V2_PROP_FACTORY_FUNCTION[]
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def quantity(storage_name): # <1>
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def qty_getter(instance): # <2>
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return instance.__dict__[storage_name] # <3>
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def qty_setter(instance, value): # <4>
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if value > 0:
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instance.__dict__[storage_name] = value # <5>
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else:
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raise ValueError('value must be > 0')
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return property(qty_getter, qty_setter) # <6>
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# end::LINEITEM_V2_PROP_FACTORY_FUNCTION[]
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# tag::LINEITEM_V2_PROP_CLASS[]
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class LineItem:
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weight = quantity('weight') # <1>
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price = quantity('price') # <2>
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def __init__(self, description, weight, price):
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self.description = description
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self.weight = weight # <3>
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self.price = price
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def subtotal(self):
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return self.weight * self.price # <4>
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# end::LINEITEM_V2_PROP_CLASS[]
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