projects / OpenSPARC-T2-SAM / blame
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| 54 | <H1><A NAME="SECTION009600000000000000000"></A><A NAME="class"></A> | |
| 55 | <BR> | |
| 56 | 7.6 Class definitions | |
| 57 | </H1> | |
| 58 | <a id='l2h-614' xml:id='l2h-614'></a><a id='l2h-615' xml:id='l2h-615'></a> | |
| 59 | <P> | |
| 60 | A class definition defines a class object (see section <A href="types.html#types">3.2</A>): | |
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| 62 | <P> | |
| 63 | <dl><dd class="grammar"> | |
| 64 | <div class="productions"> | |
| 65 | <table> | |
| 66 | <tr> | |
| 67 | <td><a id='tok-classdef' xml:id='tok-classdef'>classdef</a></td> | |
| 68 | <td>::=</td> | |
| 69 | <td>"class" <a class='grammartoken' href="class.html#tok-classname">classname</a> [<a class='grammartoken' href="class.html#tok-inheritance">inheritance</a>] ":" | |
| 70 | <a class='grammartoken' href="compound.html#tok-suite">suite</a></td></tr> | |
| 71 | <tr> | |
| 72 | <td><a id='tok-inheritance' xml:id='tok-inheritance'>inheritance</a></td> | |
| 73 | <td>::=</td> | |
| 74 | <td>"(" <a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a> ")"</td></tr> | |
| 75 | <tr> | |
| 76 | <td><a id='tok-classname' xml:id='tok-classname'>classname</a></td> | |
| 77 | <td>::=</td> | |
| 78 | <td><a class='grammartoken' href="identifiers.html#tok-identifier">identifier</a></td></tr> | |
| 79 | </table> | |
| 80 | </div> | |
| 81 | <a class="grammar-footer" | |
| 82 | href="grammar.txt" type="text/plain" | |
| 83 | >Download entire grammar as text.</a> | |
| 84 | </dd></dl> | |
| 85 | ||
| 86 | <P> | |
| 87 | A class definition is an executable statement. It first evaluates the | |
| 88 | inheritance list, if present. Each item in the inheritance list | |
| 89 | should evaluate to a class object or class type which allows | |
| 90 | subclassing. The class's suite is then executed | |
| 91 | in a new execution frame (see section <A href="naming.html#naming">4.1</A>), using a newly | |
| 92 | created local namespace and the original global namespace. | |
| 93 | (Usually, the suite contains only function definitions.) When the | |
| 94 | class's suite finishes execution, its execution frame is discarded but | |
| 95 | its local namespace is saved. A class object is then created using | |
| 96 | the inheritance list for the base classes and the saved local | |
| 97 | namespace for the attribute dictionary. The class name is bound to this | |
| 98 | class object in the original local namespace. | |
| 99 | <a id='l2h-620' xml:id='l2h-620'></a> | |
| 100 | <a id='l2h-617' xml:id='l2h-617'></a><a id='l2h-618' xml:id='l2h-618'></a><a id='l2h-619' xml:id='l2h-619'></a> | |
| 101 | <P> | |
| 102 | <strong>Programmer's note:</strong> Variables defined in the class definition | |
| 103 | are class variables; they are shared by all instances. To define | |
| 104 | instance variables, they must be given a value in the | |
| 105 | <tt class="method">__init__()</tt> method or in another method. Both class and | |
| 106 | instance variables are accessible through the notation | |
| 107 | ``<code>self.name</code>'', and an instance variable hides a class variable | |
| 108 | with the same name when accessed in this way. Class variables with | |
| 109 | immutable values can be used as defaults for instance variables. | |
| 110 | For new-style classes, descriptors can be used to create instance | |
| 111 | variables with different implementation details. | |
| 112 | ||
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| 127 | <td align="center" width="100%">Python Reference Manual</td> | |
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| 144 | </div> | |
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| 147 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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