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38 lines
1.5 KiB
XML
38 lines
1.5 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>The ability to override the class dictionary using a <code>__slots__</code> declaration
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is supported only by new-style classes. When you add a <code>__slots__</code> declaration to an
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old-style class it just creates a class attribute called '__slots__'.</p>
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</overview>
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<recommendation>
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<p>If you want to override the dictionary for a class, then ensure that the class is a new-style class.
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You can convert an old-style class to a new-style class by inheriting from <code>object</code>.</p>
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</recommendation>
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<example>
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<p>In the following example the <code>KeyedRef</code> class is an old-style class (no inheritance). The
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<code>__slots__</code> declaration in this class creates a class attribute called '__slots__', the class
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dictionary is unaffected. The <code>KeyedRef2</code> class is a new-style class so the
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<code>__slots__</code> declaration causes special compact attributes to be created for each name in
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the slots list and saves space by not creating attribute dictionaries.</p>
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<sample src="SlotsInOldStyleClass.py" />
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</example>
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<references>
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<li>Python Glossary: <a href="http://docs.python.org/glossary.html#term-new-style-class">New-style class</a>.</li>
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<li>Python Language Reference: <a href="http://docs.python.org/2/reference/datamodel.html#newstyle">New-style and classic
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classes</a>,
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<a href="http://docs.python.org/reference/datamodel.html#__slots__">__slots__</a>.</li>
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</references>
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</qhelp>
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