removed 1st edition code
This commit is contained in:
Luciano Ramalho
@@ -1,4 +0,0 @@
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Sample code for Chapter 20 - "Attribute descriptors"
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From the book "Fluent Python" by Luciano Ramalho (O'Reilly, 2015)
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http://shop.oreilly.com/product/0636920032519.do
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@@ -1,61 +0,0 @@
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"""
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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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Negative or 0 price is not acceptable either::
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>>> truffle = LineItem('White truffle', 100, 0)
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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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"""
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# BEGIN LINEITEM_V3
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class Quantity: # <1>
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def __init__(self, storage_name):
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self.storage_name = storage_name # <2>
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def __set__(self, instance, value): # <3>
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if value > 0:
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instance.__dict__[self.storage_name] = value # <4>
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else:
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raise ValueError('value must be > 0')
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class LineItem:
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weight = Quantity('weight') # <5>
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price = Quantity('price') # <6>
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def __init__(self, description, weight, price): # <7>
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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_V3
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@@ -1,74 +0,0 @@
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"""
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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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['_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, '_Quantity#1')
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6.95
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"""
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# BEGIN LINEITEM_V4
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class Quantity:
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__counter = 0 # <1>
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def __init__(self):
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cls = self.__class__ # <2>
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prefix = cls.__name__
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index = cls.__counter
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self.storage_name = '_{}#{}'.format(prefix, index) # <3>
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cls.__counter += 1 # <4>
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def __get__(self, instance, owner): # <5>
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return getattr(instance, self.storage_name) # <6>
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def __set__(self, instance, value):
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if value > 0:
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setattr(instance, self.storage_name, value) # <7>
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else:
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raise ValueError('value must be > 0')
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class LineItem:
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weight = Quantity() # <8>
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price = 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_V4
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@@ -1,85 +0,0 @@
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"""
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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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['_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, '_Quantity#1')
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6.95
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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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<bulkfood_v4b.Quantity object at 0x...>
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>>> LineItem.weight.storage_name
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'_Quantity#0'
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"""
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# BEGIN LINEITEM_V4B
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class Quantity:
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__counter = 0
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def __init__(self):
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cls = self.__class__
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prefix = cls.__name__
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index = cls.__counter
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self.storage_name = '_{}#{}'.format(prefix, index)
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cls.__counter += 1
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def __get__(self, instance, owner):
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if instance is None:
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return self # <1>
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else:
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return getattr(instance, self.storage_name) # <2>
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def __set__(self, instance, value):
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if value > 0:
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setattr(instance, self.storage_name, value)
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else:
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raise ValueError('value must be > 0')
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# END LINEITEM_V4B
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class LineItem:
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weight = Quantity()
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price = 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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@@ -1,65 +0,0 @@
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"""
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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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['_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, '_Quantity#1')
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6.95
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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_v4c.Quantity object at 0x...>
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>>> LineItem.weight.storage_name
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'_Quantity#0'
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"""
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# BEGIN LINEITEM_V4C
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import model_v4c as model # <1>
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class LineItem:
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weight = model.Quantity() # <2>
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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_V4C
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@@ -1,74 +0,0 @@
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"""
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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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[... '_quantity:0', '_quantity:1', 'description',
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'price', 'subtotal', 'weight']
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>>> getattr(raisins, '_quantity:0')
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10
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>>> getattr(raisins, '_quantity:1')
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6.95
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"""
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# BEGIN LINEITEM_V4_PROP
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def quantity(): # <1>
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try:
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quantity.counter += 1 # <2>
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except AttributeError:
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quantity.counter = 0 # <3>
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storage_name = '_{}:{}'.format('quantity', quantity.counter) # <4>
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def qty_getter(instance): # <5>
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return getattr(instance, storage_name)
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def qty_setter(instance, value):
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if value > 0:
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setattr(instance, storage_name, value)
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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)
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# END LINEITEM_V4_PROP
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class LineItem:
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weight = quantity()
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price = 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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@@ -1,79 +0,0 @@
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"""
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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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@@ -1,85 +0,0 @@
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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)
|
||||
|
||||
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; -20 is not valid.
|
||||
|
||||
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
|
||||
['_Check#0', '_Check#1', '_Check#2', '__class__', ...
|
||||
'description', 'price', 'subtotal', 'weight']
|
||||
>>> [getattr(raisins, name) for name in dir(raisins) if name.startswith('_Check#')]
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['Golden raisins', 10, 6.95]
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|
||||
If the descriptor is accessed in the class, the descriptor object is
|
||||
returned:
|
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|
||||
>>> LineItem.weight # doctest: +ELLIPSIS
|
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<model_v5_check.Check object at 0x...>
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>>> LineItem.weight.storage_name
|
||||
'_Check#1'
|
||||
|
||||
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: ' ' is not valid.
|
||||
>>> void = LineItem('', 1, 1)
|
||||
Traceback (most recent call last):
|
||||
...
|
||||
ValueError: '' is not valid.
|
||||
|
||||
|
||||
|
||||
"""
|
||||
|
||||
import model_v5_check as model
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||||
|
||||
def gt_zero(x):
|
||||
'''value must be > 0'''
|
||||
return x if x > 0 else model.INVALID
|
||||
|
||||
def non_blank(txt):
|
||||
txt = txt.strip()
|
||||
return txt if txt else model.INVALID
|
||||
|
||||
|
||||
class LineItem:
|
||||
description = model.Check(non_blank)
|
||||
weight = model.Check(gt_zero)
|
||||
price = model.Check(gt_zero)
|
||||
|
||||
def __init__(self, description, weight, price):
|
||||
self.description = description
|
||||
self.weight = weight
|
||||
self.price = price
|
||||
|
||||
def subtotal(self):
|
||||
return self.weight * self.price
|
||||
|
||||
@@ -1,23 +0,0 @@
|
||||
# BEGIN MODEL_V4
|
||||
class Quantity:
|
||||
__counter = 0
|
||||
|
||||
def __init__(self):
|
||||
cls = self.__class__
|
||||
prefix = cls.__name__
|
||||
index = cls.__counter
|
||||
self.storage_name = '_{}#{}'.format(prefix, index)
|
||||
cls.__counter += 1
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
if instance is None:
|
||||
return self
|
||||
else:
|
||||
return getattr(instance, self.storage_name)
|
||||
|
||||
def __set__(self, instance, value):
|
||||
if value > 0:
|
||||
setattr(instance, self.storage_name, value)
|
||||
else:
|
||||
raise ValueError('value must be > 0')
|
||||
# END MODEL_V4
|
||||
@@ -1,54 +0,0 @@
|
||||
# BEGIN MODEL_V5
|
||||
import abc
|
||||
|
||||
|
||||
class AutoStorage: # <1>
|
||||
__counter = 0
|
||||
|
||||
def __init__(self):
|
||||
cls = self.__class__
|
||||
prefix = cls.__name__
|
||||
index = cls.__counter
|
||||
self.storage_name = '_{}#{}'.format(prefix, index)
|
||||
cls.__counter += 1
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
if instance is None:
|
||||
return self
|
||||
else:
|
||||
return getattr(instance, self.storage_name)
|
||||
|
||||
def __set__(self, instance, value):
|
||||
setattr(instance, self.storage_name, value) # <2>
|
||||
|
||||
|
||||
class Validated(abc.ABC, AutoStorage): # <3>
|
||||
|
||||
def __set__(self, instance, value):
|
||||
value = self.validate(instance, value) # <4>
|
||||
super().__set__(instance, value) # <5>
|
||||
|
||||
@abc.abstractmethod
|
||||
def validate(self, instance, value): # <6>
|
||||
"""return validated value or raise ValueError"""
|
||||
|
||||
|
||||
class Quantity(Validated): # <7>
|
||||
"""a number greater than zero"""
|
||||
|
||||
def validate(self, instance, value):
|
||||
if value <= 0:
|
||||
raise ValueError('value must be > 0')
|
||||
return value
|
||||
|
||||
|
||||
class NonBlank(Validated):
|
||||
"""a string with at least one non-space character"""
|
||||
|
||||
def validate(self, instance, value):
|
||||
value = value.strip()
|
||||
if len(value) == 0:
|
||||
raise ValueError('value cannot be empty or blank')
|
||||
return value # <8>
|
||||
|
||||
# END MODEL_V5
|
||||
@@ -1,52 +0,0 @@
|
||||
import abc
|
||||
|
||||
|
||||
class AutoStorage:
|
||||
__counter = 0
|
||||
|
||||
def __init__(self):
|
||||
cls = self.__class__
|
||||
prefix = cls.__name__
|
||||
index = cls.__counter
|
||||
self.storage_name = '_{}#{}'.format(prefix, index)
|
||||
cls.__counter += 1
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
if instance is None:
|
||||
return self
|
||||
else:
|
||||
return getattr(instance, self.storage_name)
|
||||
|
||||
def __set__(self, instance, value):
|
||||
setattr(instance, self.storage_name, value)
|
||||
|
||||
|
||||
class Validated(abc.ABC, AutoStorage):
|
||||
|
||||
def __set__(self, instance, value):
|
||||
value = self.validate(instance, value)
|
||||
super().__set__(instance, value)
|
||||
|
||||
@abc.abstractmethod
|
||||
def validate(self, instance, value):
|
||||
"""return validated value or raise ValueError"""
|
||||
|
||||
INVALID = object()
|
||||
|
||||
class Check(Validated):
|
||||
|
||||
def __init__(self, checker):
|
||||
super().__init__()
|
||||
self.checker = checker
|
||||
if checker.__doc__ is None:
|
||||
doc = ''
|
||||
else:
|
||||
doc = checker.__doc__ + '; '
|
||||
self.message = doc + '{!r} is not valid.'
|
||||
|
||||
|
||||
def validate(self, instance, value):
|
||||
result = self.checker(value)
|
||||
if result is INVALID:
|
||||
raise ValueError(self.message.format(value))
|
||||
return result
|
||||
@@ -1,199 +0,0 @@
|
||||
"""
|
||||
Overriding descriptor (a.k.a. data descriptor or enforced descriptor):
|
||||
|
||||
# BEGIN DESCR_KINDS_DEMO1
|
||||
|
||||
>>> obj = Managed() # <1>
|
||||
>>> obj.over # <2>
|
||||
-> Overriding.__get__(<Overriding object>, <Managed object>, <class Managed>)
|
||||
>>> Managed.over # <3>
|
||||
-> Overriding.__get__(<Overriding object>, None, <class Managed>)
|
||||
>>> obj.over = 7 # <4>
|
||||
-> Overriding.__set__(<Overriding object>, <Managed object>, 7)
|
||||
>>> obj.over # <5>
|
||||
-> Overriding.__get__(<Overriding object>, <Managed object>, <class Managed>)
|
||||
>>> obj.__dict__['over'] = 8 # <6>
|
||||
>>> vars(obj) # <7>
|
||||
{'over': 8}
|
||||
>>> obj.over # <8>
|
||||
-> Overriding.__get__(<Overriding object>, <Managed object>, <class Managed>)
|
||||
|
||||
# END DESCR_KINDS_DEMO1
|
||||
|
||||
Overriding descriptor without ``__get__``:
|
||||
|
||||
(these tests are reproduced below without +ELLIPSIS directives for inclusion in the book;
|
||||
look for DESCR_KINDS_DEMO2)
|
||||
|
||||
>>> obj.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
>>> Managed.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
>>> obj.over_no_get = 7
|
||||
-> OverridingNoGet.__set__(<OverridingNoGet object>, <Managed object>, 7)
|
||||
>>> obj.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
>>> obj.__dict__['over_no_get'] = 9
|
||||
>>> obj.over_no_get
|
||||
9
|
||||
>>> obj.over_no_get = 7
|
||||
-> OverridingNoGet.__set__(<OverridingNoGet object>, <Managed object>, 7)
|
||||
>>> obj.over_no_get
|
||||
9
|
||||
|
||||
Non-overriding descriptor (a.k.a. non-data descriptor or shadowable descriptor):
|
||||
|
||||
# BEGIN DESCR_KINDS_DEMO3
|
||||
|
||||
>>> obj = Managed()
|
||||
>>> obj.non_over # <1>
|
||||
-> NonOverriding.__get__(<NonOverriding object>, <Managed object>, <class Managed>)
|
||||
>>> obj.non_over = 7 # <2>
|
||||
>>> obj.non_over # <3>
|
||||
7
|
||||
>>> Managed.non_over # <4>
|
||||
-> NonOverriding.__get__(<NonOverriding object>, None, <class Managed>)
|
||||
>>> del obj.non_over # <5>
|
||||
>>> obj.non_over # <6>
|
||||
-> NonOverriding.__get__(<NonOverriding object>, <Managed object>, <class Managed>)
|
||||
|
||||
# END DESCR_KINDS_DEMO3
|
||||
|
||||
No descriptor type survives being overwritten on the class itself:
|
||||
|
||||
# BEGIN DESCR_KINDS_DEMO4
|
||||
|
||||
>>> obj = Managed() # <1>
|
||||
>>> Managed.over = 1 # <2>
|
||||
>>> Managed.over_no_get = 2
|
||||
>>> Managed.non_over = 3
|
||||
>>> obj.over, obj.over_no_get, obj.non_over # <3>
|
||||
(1, 2, 3)
|
||||
|
||||
# END DESCR_KINDS_DEMO4
|
||||
|
||||
Methods are non-overriding descriptors:
|
||||
|
||||
>>> obj.spam # doctest: +ELLIPSIS
|
||||
<bound method Managed.spam of <descriptorkinds.Managed object at 0x...>>
|
||||
>>> Managed.spam # doctest: +ELLIPSIS
|
||||
<function Managed.spam at 0x...>
|
||||
>>> obj.spam()
|
||||
-> Managed.spam(<Managed object>)
|
||||
>>> Managed.spam()
|
||||
Traceback (most recent call last):
|
||||
...
|
||||
TypeError: spam() missing 1 required positional argument: 'self'
|
||||
>>> Managed.spam(obj)
|
||||
-> Managed.spam(<Managed object>)
|
||||
>>> Managed.spam.__get__(obj) # doctest: +ELLIPSIS
|
||||
<bound method Managed.spam of <descriptorkinds.Managed object at 0x...>>
|
||||
>>> obj.spam.__func__ is Managed.spam
|
||||
True
|
||||
>>> obj.spam = 7
|
||||
>>> obj.spam
|
||||
7
|
||||
|
||||
|
||||
"""
|
||||
|
||||
"""
|
||||
NOTE: These tests are here because I can't add callouts after +ELLIPSIS
|
||||
directives and if doctest runs them without +ELLIPSIS I get test failures.
|
||||
|
||||
# BEGIN DESCR_KINDS_DEMO2
|
||||
|
||||
>>> obj.over_no_get # <1>
|
||||
<__main__.OverridingNoGet object at 0x665bcc>
|
||||
>>> Managed.over_no_get # <2>
|
||||
<__main__.OverridingNoGet object at 0x665bcc>
|
||||
>>> obj.over_no_get = 7 # <3>
|
||||
-> OverridingNoGet.__set__(<OverridingNoGet object>, <Managed object>, 7)
|
||||
>>> obj.over_no_get # <4>
|
||||
<__main__.OverridingNoGet object at 0x665bcc>
|
||||
>>> obj.__dict__['over_no_get'] = 9 # <5>
|
||||
>>> obj.over_no_get # <6>
|
||||
9
|
||||
>>> obj.over_no_get = 7 # <7>
|
||||
-> OverridingNoGet.__set__(<OverridingNoGet object>, <Managed object>, 7)
|
||||
>>> obj.over_no_get # <8>
|
||||
9
|
||||
|
||||
# END DESCR_KINDS_DEMO2
|
||||
|
||||
Methods are non-overriding descriptors:
|
||||
|
||||
# BEGIN DESCR_KINDS_DEMO5
|
||||
|
||||
>>> obj = Managed()
|
||||
>>> obj.spam # <1>
|
||||
<bound method Managed.spam of <descriptorkinds.Managed object at 0x74c80c>>
|
||||
>>> Managed.spam # <2>
|
||||
<function Managed.spam at 0x734734>
|
||||
>>> obj.spam = 7 # <3>
|
||||
>>> obj.spam
|
||||
7
|
||||
|
||||
# END DESCR_KINDS_DEMO5
|
||||
|
||||
"""
|
||||
|
||||
# BEGIN DESCR_KINDS
|
||||
|
||||
### auxiliary functions for display only ###
|
||||
|
||||
def cls_name(obj_or_cls):
|
||||
cls = type(obj_or_cls)
|
||||
if cls is type:
|
||||
cls = obj_or_cls
|
||||
return cls.__name__.split('.')[-1]
|
||||
|
||||
def display(obj):
|
||||
cls = type(obj)
|
||||
if cls is type:
|
||||
return '<class {}>'.format(obj.__name__)
|
||||
elif cls in [type(None), int]:
|
||||
return repr(obj)
|
||||
else:
|
||||
return '<{} object>'.format(cls_name(obj))
|
||||
|
||||
def print_args(name, *args):
|
||||
pseudo_args = ', '.join(display(x) for x in args)
|
||||
print('-> {}.__{}__({})'.format(cls_name(args[0]), name, pseudo_args))
|
||||
|
||||
|
||||
### essential classes for this example ###
|
||||
|
||||
class Overriding: # <1>
|
||||
"""a.k.a. data descriptor or enforced descriptor"""
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
print_args('get', self, instance, owner) # <2>
|
||||
|
||||
def __set__(self, instance, value):
|
||||
print_args('set', self, instance, value)
|
||||
|
||||
|
||||
class OverridingNoGet: # <3>
|
||||
"""an overriding descriptor without ``__get__``"""
|
||||
|
||||
def __set__(self, instance, value):
|
||||
print_args('set', self, instance, value)
|
||||
|
||||
|
||||
class NonOverriding: # <4>
|
||||
"""a.k.a. non-data or shadowable descriptor"""
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
print_args('get', self, instance, owner)
|
||||
|
||||
|
||||
class Managed: # <5>
|
||||
over = Overriding()
|
||||
over_no_get = OverridingNoGet()
|
||||
non_over = NonOverriding()
|
||||
|
||||
def spam(self): # <6>
|
||||
print('-> Managed.spam({})'.format(display(self)))
|
||||
|
||||
# END DESCR_KINDS
|
||||
@@ -1,169 +0,0 @@
|
||||
|
||||
|
||||
"""
|
||||
Overriding descriptor (a.k.a. data descriptor or enforced descriptor):
|
||||
|
||||
>>> obj = Model()
|
||||
>>> obj.over # doctest: +ELLIPSIS
|
||||
Overriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.Overriding object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
>>> Model.over # doctest: +ELLIPSIS
|
||||
Overriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.Overriding object at 0x...>
|
||||
instance = None
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
|
||||
|
||||
An overriding descriptor cannot be shadowed by assigning to an instance:
|
||||
|
||||
>>> obj = Model()
|
||||
>>> obj.over = 7 # doctest: +ELLIPSIS
|
||||
Overriding.__set__() invoked with args:
|
||||
self = <descriptorkinds.Overriding object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
value = 7
|
||||
>>> obj.over # doctest: +ELLIPSIS
|
||||
Overriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.Overriding object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
|
||||
|
||||
Not even by poking the attribute into the instance ``__dict__``:
|
||||
|
||||
>>> obj.__dict__['over'] = 8
|
||||
>>> obj.over # doctest: +ELLIPSIS
|
||||
Overriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.Overriding object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
>>> vars(obj)
|
||||
{'over': 8}
|
||||
|
||||
Overriding descriptor without ``__get__``:
|
||||
|
||||
>>> obj.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
>>> Model.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
>>> obj.over_no_get = 7 # doctest: +ELLIPSIS
|
||||
OverridingNoGet.__set__() invoked with args:
|
||||
self = <descriptorkinds.OverridingNoGet object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
value = 7
|
||||
>>> obj.over_no_get # doctest: +ELLIPSIS
|
||||
<descriptorkinds.OverridingNoGet object at 0x...>
|
||||
|
||||
|
||||
Poking the attribute into the instance ``__dict__`` means you can read the new
|
||||
value for the attribute, but setting it still triggers ``__set__``:
|
||||
|
||||
>>> obj.__dict__['over_no_get'] = 9
|
||||
>>> obj.over_no_get
|
||||
9
|
||||
>>> obj.over_no_get = 7 # doctest: +ELLIPSIS
|
||||
OverridingNoGet.__set__() invoked with args:
|
||||
self = <descriptorkinds.OverridingNoGet object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
value = 7
|
||||
>>> obj.over_no_get
|
||||
9
|
||||
|
||||
|
||||
Non-overriding descriptor (a.k.a. non-data descriptor or shadowable descriptor):
|
||||
|
||||
>>> obj = Model()
|
||||
>>> obj.non_over # doctest: +ELLIPSIS
|
||||
NonOverriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.NonOverriding object at 0x...>
|
||||
instance = <descriptorkinds.Model object at 0x...>
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
>>> Model.non_over # doctest: +ELLIPSIS
|
||||
NonOverriding.__get__() invoked with args:
|
||||
self = <descriptorkinds.NonOverriding object at 0x...>
|
||||
instance = None
|
||||
owner = <class 'descriptorkinds.Model'>
|
||||
|
||||
|
||||
A non-overriding descriptor can be shadowed by assigning to an instance:
|
||||
|
||||
>>> obj.non_over = 7
|
||||
>>> obj.non_over
|
||||
7
|
||||
|
||||
|
||||
Methods are non-over descriptors:
|
||||
|
||||
>>> obj.spam # doctest: +ELLIPSIS
|
||||
<bound method Model.spam of <descriptorkinds.Model object at 0x...>>
|
||||
>>> Model.spam # doctest: +ELLIPSIS
|
||||
<function Model.spam at 0x...>
|
||||
>>> obj.spam() # doctest: +ELLIPSIS
|
||||
Model.spam() invoked with arg:
|
||||
self = <descriptorkinds.Model object at 0x...>
|
||||
>>> obj.spam = 7
|
||||
>>> obj.spam
|
||||
7
|
||||
|
||||
|
||||
No descriptor type survives being overwritten on the class itself:
|
||||
|
||||
>>> Model.over = 1
|
||||
>>> obj.over
|
||||
1
|
||||
>>> Model.over_no_get = 2
|
||||
>>> obj.over_no_get
|
||||
2
|
||||
>>> Model.non_over = 3
|
||||
>>> obj.non_over
|
||||
7
|
||||
|
||||
"""
|
||||
|
||||
# BEGIN DESCRIPTORKINDS
|
||||
def print_args(name, *args): # <1>
|
||||
cls_name = args[0].__class__.__name__
|
||||
arg_names = ['self', 'instance', 'owner']
|
||||
if name == 'set':
|
||||
arg_names[-1] = 'value'
|
||||
print('{}.__{}__() invoked with args:'.format(cls_name, name))
|
||||
for arg_name, value in zip(arg_names, args):
|
||||
print(' {:8} = {}'.format(arg_name, value))
|
||||
|
||||
|
||||
class Overriding: # <2>
|
||||
"""a.k.a. data descriptor or enforced descriptor"""
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
print_args('get', self, instance, owner) # <3>
|
||||
|
||||
def __set__(self, instance, value):
|
||||
print_args('set', self, instance, value)
|
||||
|
||||
|
||||
class OverridingNoGet: # <4>
|
||||
"""an overriding descriptor without ``__get__``"""
|
||||
|
||||
def __set__(self, instance, value):
|
||||
print_args('set', self, instance, value)
|
||||
|
||||
|
||||
class NonOverriding: # <5>
|
||||
"""a.k.a. non-data or shadowable descriptor"""
|
||||
|
||||
def __get__(self, instance, owner):
|
||||
print_args('get', self, instance, owner)
|
||||
|
||||
|
||||
class Model: # <6>
|
||||
over = Overriding()
|
||||
over_no_get = OverridingNoGet()
|
||||
non_over = NonOverriding()
|
||||
|
||||
def spam(self): # <7>
|
||||
print('Model.spam() invoked with arg:')
|
||||
print(' self =', self)
|
||||
|
||||
#END DESCRIPTORKINDS
|
||||
@@ -1,41 +0,0 @@
|
||||
"""
|
||||
# BEGIN FUNC_DESCRIPTOR_DEMO
|
||||
|
||||
>>> word = Text('forward')
|
||||
>>> word # <1>
|
||||
Text('forward')
|
||||
>>> word.reverse() # <2>
|
||||
Text('drawrof')
|
||||
>>> Text.reverse(Text('backward')) # <3>
|
||||
Text('drawkcab')
|
||||
>>> type(Text.reverse), type(word.reverse) # <4>
|
||||
(<class 'function'>, <class 'method'>)
|
||||
>>> list(map(Text.reverse, ['repaid', (10, 20, 30), Text('stressed')])) # <5>
|
||||
['diaper', (30, 20, 10), Text('desserts')]
|
||||
>>> Text.reverse.__get__(word) # <6>
|
||||
<bound method Text.reverse of Text('forward')>
|
||||
>>> Text.reverse.__get__(None, Text) # <7>
|
||||
<function Text.reverse at 0x101244e18>
|
||||
>>> word.reverse # <8>
|
||||
<bound method Text.reverse of Text('forward')>
|
||||
>>> word.reverse.__self__ # <9>
|
||||
Text('forward')
|
||||
>>> word.reverse.__func__ is Text.reverse # <10>
|
||||
True
|
||||
|
||||
# END FUNC_DESCRIPTOR_DEMO
|
||||
"""
|
||||
|
||||
# BEGIN FUNC_DESCRIPTOR_EX
|
||||
import collections
|
||||
|
||||
|
||||
class Text(collections.UserString):
|
||||
|
||||
def __repr__(self):
|
||||
return 'Text({!r})'.format(self.data)
|
||||
|
||||
def reverse(self):
|
||||
return self[::-1]
|
||||
|
||||
# END FUNC_DESCRIPTOR_EX
|
||||
Reference in New Issue
Block a user