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<overview>

<p>Property descriptors are only supported for the new-style classes that were introduced in Python

2.1. Property descriptors should only be used in new-style classes.</p>

</overview>

<recommendation>

<p>If you want to define properties in a class, then ensure that the class is a new-style class. You can

convert an old-style class to a new-style class by inheriting from <code>object</code>.</p>

</recommendation>

<example>

<p>In the following example all the classes attempt to set a property for <code>x</code>. However, only

the third and fourth classes are new-style classes. Consequently, the <code>x</code>

property is only available for the <code>NewStyle</code> and <code>InheritNewStyle</code> classes.</p>

<p>If you define the <code>OldStyle</code> class as inheriting from a new-style class, then the <code>x

</code> property would be available for both the <code>OldStyle</code> and <code>InheritOldStyle</code> classes.</p>

<sample src="PropertyInOldStyleClass.py" />

</example>

<references>

<li>Python Glossary: <a href="http://docs.python.org/glossary.html#term-new-style-class">New-style class</a>.</li>

<li>Python Language Reference: <a href="http://docs.python.org/2/reference/datamodel.html#newstyle">New-style and classic

classes</a>,

<a href="http://docs.python.org/2/reference/datamodel.html#implementing-descriptors">

Descriptors</a>.</li>

<li>Python Standard Library: <a href="http://docs.python.org/library/functions.html#property">Property</a>.</li>

<li>The History of Python: <a href="http://python-history.blogspot.co.uk/2010/06/inside-story-on-new-style-classes.html">

Inside story on new-style classes</a>.</li>

</references>

</qhelp>