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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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| 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> |
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| 98 | <LI><A href="numeric-types.html">3.3.7 Emulating numeric types</a> |
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