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| 54 | 2.2.3 Attribute Management</A> |
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| 56 | |
| 57 | <P> |
| 58 | For every object which can support attributes, the corresponding type |
| 59 | must provide the functions that control how the attributes are |
| 60 | resolved. There needs to be a function which can retrieve attributes |
| 61 | (if any are defined), and another to set attributes (if setting |
| 62 | attributes is allowed). Removing an attribute is a special case, for |
| 63 | which the new value passed to the handler is <tt class="constant">NULL</tt>. |
| 64 | |
| 65 | <P> |
| 66 | Python supports two pairs of attribute handlers; a type that supports |
| 67 | attributes only needs to implement the functions for one pair. The |
| 68 | difference is that one pair takes the name of the attribute as a |
| 69 | <tt class="ctype">char*</tt>, while the other accepts a <tt class="ctype">PyObject*</tt>. Each type |
| 70 | can use whichever pair makes more sense for the implementation's |
| 71 | convenience. |
| 72 | |
| 73 | <P> |
| 74 | <div class="verbatim"><pre> |
| 75 | getattrfunc tp_getattr; /* char * version */ |
| 76 | setattrfunc tp_setattr; |
| 77 | /* ... */ |
| 78 | getattrofunc tp_getattrofunc; /* PyObject * version */ |
| 79 | setattrofunc tp_setattrofunc; |
| 80 | </pre></div> |
| 81 | |
| 82 | <P> |
| 83 | If accessing attributes of an object is always a simple operation |
| 84 | (this will be explained shortly), there are generic implementations |
| 85 | which can be used to provide the <tt class="ctype">PyObject*</tt> version of the |
| 86 | attribute management functions. The actual need for type-specific |
| 87 | attribute handlers almost completely disappeared starting with Python |
| 88 | 2.2, though there are many examples which have not been updated to use |
| 89 | some of the new generic mechanism that is available. |
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| 99 | <LI><A href="node29.html">2.2.3.1 Generic Attribute Management</a> |
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