projects / OpenSPARC-T2-SAM / blame
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| 54 | ||
| 55 | <H1><A NAME="SECTION008900000000000000000"></A><A NAME="raise"></A> | |
| 56 | <BR> | |
| 57 | 6.9 The <tt class="keyword">raise</tt> statement | |
| 58 | </H1> | |
| 59 | <a id='l2h-513' xml:id='l2h-513'></a> | |
| 60 | <P> | |
| 61 | <dl><dd class="grammar"> | |
| 62 | <div class="productions"> | |
| 63 | <table> | |
| 64 | <tr> | |
| 65 | <td><a id='tok-raise_stmt' xml:id='tok-raise_stmt'>raise_stmt</a></td> | |
| 66 | <td>::=</td> | |
| 67 | <td>"raise" [<a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ["," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> | |
| 68 | ["," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a>]]]</td></tr> | |
| 69 | </table> | |
| 70 | </div> | |
| 71 | <a class="grammar-footer" | |
| 72 | href="grammar.txt" type="text/plain" | |
| 73 | >Download entire grammar as text.</a> | |
| 74 | </dd></dl> | |
| 75 | ||
| 76 | <P> | |
| 77 | If no expressions are present, <tt class="keyword">raise</tt> re-raises the last | |
| 78 | exception that was active in the current scope. If no exception is | |
| 79 | active in the current scope, a <tt class="exception">Queue.Empty</tt> exception is | |
| 80 | raised indicating this error. | |
| 81 | <a id='l2h-516' xml:id='l2h-516'></a> | |
| 82 | <a id='l2h-514' xml:id='l2h-514'></a> | |
| 83 | <P> | |
| 84 | Otherwise, <tt class="keyword">raise</tt> evaluates the expressions to get three | |
| 85 | objects, using <code>None</code> as the value of omitted expressions. The | |
| 86 | first two objects are used to determine the <em>type</em> and | |
| 87 | <em>value</em> of the exception. | |
| 88 | ||
| 89 | <P> | |
| 90 | If the first object is an instance, the type of the exception is the | |
| 91 | class of the instance, the instance itself is the value, and the | |
| 92 | second object must be <code>None</code>. | |
| 93 | ||
| 94 | <P> | |
| 95 | If the first object is a class, it becomes the type of the exception. | |
| 96 | The second object is used to determine the exception value: If it is | |
| 97 | an instance of the class, the instance becomes the exception value. | |
| 98 | If the second object is a tuple, it is used as the argument list for | |
| 99 | the class constructor; if it is <code>None</code>, an empty argument list is | |
| 100 | used, and any other object is treated as a single argument to the | |
| 101 | constructor. The instance so created by calling the constructor is | |
| 102 | used as the exception value. | |
| 103 | ||
| 104 | <P> | |
| 105 | If a third object is present and not <code>None</code>, it must be a | |
| 106 | traceback<a id='l2h-515' xml:id='l2h-515'></a> object (see section <A href="types.html#traceback">3.2</A>), and | |
| 107 | it is substituted instead of the current location as the place where | |
| 108 | the exception occurred. If the third object is present and not a | |
| 109 | traceback object or <code>None</code>, a <tt class="exception">TypeError</tt> exception is | |
| 110 | raised. The three-expression form of <tt class="keyword">raise</tt> is useful to | |
| 111 | re-raise an exception transparently in an except clause, but | |
| 112 | <tt class="keyword">raise</tt> with no expressions should be preferred if the | |
| 113 | exception to be re-raised was the most recently active exception in | |
| 114 | the current scope. | |
| 115 | ||
| 116 | <P> | |
| 117 | Additional information on exceptions can be found in | |
| 118 | section <A href="exceptions.html#exceptions">4.2</A>, and information about handling exceptions is | |
| 119 | in section <A href="try.html#try">7.4</A>. | |
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| 157 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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