projects / OpenSPARC-T2-SAM / blame
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| 55 | <H3><A NAME="SECTION005322000000000000000"></A><A NAME="descriptors"></A> | |
| 56 | <BR> | |
| 57 | 3.3.2.2 Implementing Descriptors | |
| 58 | </H3> | |
| 59 | ||
| 60 | <P> | |
| 61 | The following methods only apply when an instance of the class | |
| 62 | containing the method (a so-called <em>descriptor</em> class) appears in | |
| 63 | the class dictionary of another new-style class, known as the | |
| 64 | <em>owner</em> class. In the examples below, ``the attribute'' refers to | |
| 65 | the attribute whose name is the key of the property in the owner | |
| 66 | class' <code>__dict__</code>. Descriptors can only be implemented as | |
| 67 | new-style classes themselves. | |
| 68 | ||
| 69 | <P> | |
| 70 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 71 | <td><nobr><b><tt id='l2h-214' xml:id='l2h-214' class="method">__get__</tt></b>(</nobr></td> | |
| 72 | <td><var>self, instance, owner</var>)</td></tr></table></dt> | |
| 73 | <dd> | |
| 74 | Called to get the attribute of the owner class (class attribute access) | |
| 75 | or of an instance of that class (instance attribute access). | |
| 76 | <var>owner</var> is always the owner class, while <var>instance</var> is the | |
| 77 | instance that the attribute was accessed through, or <code>None</code> when | |
| 78 | the attribute is accessed through the <var>owner</var>. This method should | |
| 79 | return the (computed) attribute value or raise an | |
| 80 | <tt class="exception">AttributeError</tt> exception. | |
| 81 | </dl> | |
| 82 | ||
| 83 | <P> | |
| 84 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 85 | <td><nobr><b><tt id='l2h-215' xml:id='l2h-215' class="method">__set__</tt></b>(</nobr></td> | |
| 86 | <td><var>self, instance, value</var>)</td></tr></table></dt> | |
| 87 | <dd> | |
| 88 | Called to set the attribute on an instance <var>instance</var> of the owner | |
| 89 | class to a new value, <var>value</var>. | |
| 90 | </dl> | |
| 91 | ||
| 92 | <P> | |
| 93 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 94 | <td><nobr><b><tt id='l2h-216' xml:id='l2h-216' class="method">__delete__</tt></b>(</nobr></td> | |
| 95 | <td><var>self, instance</var>)</td></tr></table></dt> | |
| 96 | <dd> | |
| 97 | Called to delete the attribute on an instance <var>instance</var> of the | |
| 98 | owner class. | |
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