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<h3>Defining New Types</h3>
<p>New types of objects can also be defined in extension modules. However, this process is considerably more advanced than simply accessing a few C functions. Because of this complexity, you should consider implementing a new type only in the following situations:</p>
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<p>The type is not easily constructed from existing Python types.</p>
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<P>The type requires interaction with the operating system or another special feature not provided by the interpreter or the standard library.</P>
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<P>The type hasn抰 already been implemented elsewhere. For example, efficient matrix types have already been implemented, so it would make little sense to reinvent them. It抯 always a good idea to check the Python libraries and newsgroups before implementing a new type. The Vaults of Parnassas Python Resources (<A TArget="_blank" href="http://www.vex.net/parnassus">http://www.vex.net/parnassus</a>) is also an excellent resource for finding previously implemented extension modules.</p>
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<p>The process of creating a new Python type involves the following steps:</p>
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<p>Define a data structure that contains the actual data stored in the type梖or example, the <tt cLASS="monofont">List</tt> type has an array of elements containing the list items.</p>
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<P>Define the functions that are going to serve as methods of the type梖or example, the <TT Class="monofont">append()</tt> method of a <tt class="monofont">List</tt> object.</p>
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<p>Define a pair of functions for creating and destroying the type.</p>
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<P>Define a set of functions that implement the special methods such as <TT Class="monofont">_ _add_ _()</TT> and <TT clasS="monofont">_ _getitem_ _()</TT> that are supported by the type, as described in <A href="33.html">Chapter 3</A>, 揟ypes and Objects.⌨️ 快捷键说明
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