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copied!<p>From the <a href="http://docs.python.org/reference/datamodel.html#implementing-descriptors" rel="nofollow noreferrer">documentation</a>:</p> <blockquote> <p>The following methods only apply when an instance of the class containing the method (a so-called descriptor class) appears in an owner class (the descriptor must be in either the owner’s class dictionary or in the class dictionary for one of its parents).</p> </blockquote> <p>So descriptors (ie. objects that implement <code>__get__</code>, <code>__set__</code> or <code>__delete__</code>) must be members of a class, NOT an instance.</p> <p>With the followinging changes:</p> <pre><code>Temperature.celsius2 = Celsius() T = Temperature() print('T.celsius:', T.celsius) print('T.celsius1:', T.celsius1) print('T.celsius2:', T.celsius2) </code></pre> <p>The output is:</p> <pre><code>T.celsius: 0.0 T.celsius1: <__main__.Celsius object at 0x7fab8c8d0fd0> T.celsius2:, 0.0 </code></pre> <p>More links:</p> <ul> <li><a href="http://docs.python.org/howto/descriptor.html" rel="nofollow noreferrer">Descriptor HowTo Guide</a>.</li> <li><a href="https://stackoverflow.com/questions/3798835/understanding-get-and-set-and-python-descriptors">Understanding __get__ and __set__ and Python descriptors</a></li> <li><a href="http://martyalchin.com/2007/nov/23/python-descriptors-part-1-of-2/" rel="nofollow noreferrer">http://martyalchin.com/2007/nov/23/python-descriptors-part-1-of-2/</a></li> <li><a href="https://www.google.com/?q=python%20descriptors" rel="nofollow noreferrer">https://www.google.com/?q=python%20descriptors</a></li> </ul>

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