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