projects / OpenSPARC-T2-SAM / blame
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| 16 | <title>3.3 Special method names</title> | |
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| 54 | <H1><A NAME="SECTION005300000000000000000"></A><A NAME="specialnames"></A> | |
| 55 | <BR> | |
| 56 | 3.3 Special method names | |
| 57 | </H1> | |
| 58 | ||
| 59 | <P> | |
| 60 | A class can implement certain operations that are invoked by special | |
| 61 | syntax (such as arithmetic operations or subscripting and slicing) by | |
| 62 | defining methods with special names.<a id='l2h-169' xml:id='l2h-169'></a>This is Python's approach to <i class="dfn">operator overloading</i>, allowing | |
| 63 | classes to define their own behavior with respect to language | |
| 64 | operators. For instance, if a class defines | |
| 65 | a method named <tt class="method">__getitem__()</tt>, and <code>x</code> is an instance of | |
| 66 | this class, then <code>x[i]</code> is equivalent to | |
| 67 | <code>x.__getitem__(i)</code>. Except where mentioned, attempts to execute | |
| 68 | an operation raise an exception when no appropriate method is defined. | |
| 69 | <a id='l2h-171' xml:id='l2h-171'></a> | |
| 70 | <P> | |
| 71 | When implementing a class that emulates any built-in type, it is | |
| 72 | important that the emulation only be implemented to the degree that it | |
| 73 | makes sense for the object being modelled. For example, some | |
| 74 | sequences may work well with retrieval of individual elements, but | |
| 75 | extracting a slice may not make sense. (One example of this is the | |
| 76 | <tt class="class">NodeList</tt> interface in the W3C's Document Object Model.) | |
| 77 | ||
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| 82 | <!--Table of Child-Links--> | |
| 83 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> | |
| 84 | ||
| 85 | <UL CLASS="ChildLinks"> | |
| 86 | <LI><A href="customization.html">3.3.1 Basic customization</a> | |
| 87 | <LI><A href="attribute-access.html">3.3.2 Customizing attribute access</a> | |
| 88 | <UL> | |
| 89 | <LI><A href="new-style-attribute-access.html">3.3.2.1 More attribute access for new-style classes</a> | |
| 90 | <LI><A href="descriptors.html">3.3.2.2 Implementing Descriptors</a> | |
| 91 | <LI><A href="descriptor-invocation.html">3.3.2.3 Invoking Descriptors</a> | |
| 92 | <LI><A href="slots.html">3.3.2.4 __slots__</a> | |
| 93 | </ul> | |
| 94 | <LI><A href="metaclasses.html">3.3.3 Customizing class creation</a> | |
| 95 | <LI><A href="callable-types.html">3.3.4 Emulating callable objects</a> | |
| 96 | <LI><A href="sequence-types.html">3.3.5 Emulating container types</a> | |
| 97 | <LI><A href="sequence-methods.html">3.3.6 Additional methods for emulation of sequence types</a> | |
| 98 | <LI><A href="numeric-types.html">3.3.7 Emulating numeric types</a> | |
| 99 | <LI><A href="coercion-rules.html">3.3.8 Coercion rules</a> | |
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| 109 | <td class='online-navigation'><a rel="prev" title="3.2 The standard type" | |
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| 111 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 112 | <td class='online-navigation'><a rel="parent" title="3. Data model" | |
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| 118 | <td align="center" width="100%">Python Reference Manual</td> | |
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| 129 | <b class="navlabel">Previous:</b> | |
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| 134 | <a class="sectref" rel="next" href="customization.html">3.3.1 Basic customization</A> | |
| 135 | </div> | |
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| 138 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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