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    <p>There is only one descriptor object, stored on the class object, so <code>self</code> is always the same. If you want to store data per-object and access it through the descriptor, you either have to store the data on each object (probably the better idea) or in some data-structure keyed by each object (an idea I don't like as much).</p> <p>I would save data on the instance object: </p> <pre><code>class Desc(object): default_value = 10 def __init__(self, name): self.name = name def __get__(self,obj,objtype): return obj.__dict__.get(self.name, self.default_value) # alternatively the following; but won't work with shadowing: #return getattr(obj, self.name, self.default_value) def __set__(self,obj,val): obj.__dict__[self.name] = val # alternatively the following; but won't work with shadowing: #setattr(obj, self.name, val) def __delete__(self,obj): pass class MyClass(object): desc = Desc('varx') </code></pre> <p>In this case, the data will be stored in the <code>obj</code>'s 'varx' entry in its <code>__dict__</code>. Because of how data descriptor lookup works though, you can "shadow" the storage location with the descriptor:</p> <pre><code>class MyClass(object): varx = Desc('varx') </code></pre> <p>In this case, when you do the lookup:</p> <pre><code>MyClass().varx </code></pre> <p>The descriptor object gets called and can do its lookup, but when the lookup goes like this:</p> <pre><code>MyClass().__dict__['varx'] </code></pre> <p>The value is returned directly. Thus the descriptor is able to store its data in a 'hidden' place, so to speak.</p>
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    1. POpython descriptors sharing values across classes
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    1. USMatt Anderson
    1. USMatt Anderson
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    1. POpython descriptors sharing values across classes
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    1. COI think part of the problem is that there is an example on python.org which is basically wrong for the same reason. It is the Descriptor Example in http://docs.python.org/howto/descriptor.html and is the first result when googling 'descriptors python'.
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