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<qhelp>

<overview>

<p>The ability to override the class dictionary using a <code>__slots__</code> declaration

is supported only by new-style classes. When you add a <code>__slots__</code> declaration to an

old-style class it just creates a class attribute called <code>__slots__</code>.</p>

</overview>

<recommendation>

<p>If you want to override the dictionary for 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 Python 2 example the <code>Point</code> class is an old-style class (no inheritance). The

<code>__slots__</code> declaration in this class creates a class attribute called <code>__slots__</code>, the class

dictionary is unaffected. The <code>Point2</code> class is a new-style class so the

<code>__slots__</code> declaration causes special compact attributes to be created for each name in

the slots list and saves space by not creating attribute dictionaries.</p>

<sample src="SlotsInOldStyleClass.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/reference/datamodel.html#__slots__">__slots__</a>.</li>

</references>

</qhelp>