projects / OpenSPARC-T2-SAM / blame
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| 54 | ||
| 55 | <H1><A NAME="SECTION008200000000000000000"></A><A NAME="assert"></A> | |
| 56 | <BR> | |
| 57 | 6.2 Assert statements | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | Assert statements<a id='l2h-461' xml:id='l2h-461'></a> are a convenient way to insert | |
| 62 | debugging assertions<a id='l2h-462' xml:id='l2h-462'></a> into a program: | |
| 63 | ||
| 64 | <P> | |
| 65 | <dl><dd class="grammar"> | |
| 66 | <div class="productions"> | |
| 67 | <table> | |
| 68 | <tr> | |
| 69 | <td><a id='tok-assert_stmt' xml:id='tok-assert_stmt'>assert_stmt</a></td> | |
| 70 | <td>::=</td> | |
| 71 | <td>"assert" <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ["," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a>]</td></tr> | |
| 72 | </table> | |
| 73 | </div> | |
| 74 | <a class="grammar-footer" | |
| 75 | href="grammar.txt" type="text/plain" | |
| 76 | >Download entire grammar as text.</a> | |
| 77 | </dd></dl> | |
| 78 | ||
| 79 | <P> | |
| 80 | The simple form, "<tt class="samp">assert expression</tt>", is equivalent to | |
| 81 | ||
| 82 | <P> | |
| 83 | <div class="verbatim"><pre> | |
| 84 | if __debug__: | |
| 85 | if not expression: raise AssertionError | |
| 86 | </pre></div> | |
| 87 | ||
| 88 | <P> | |
| 89 | The extended form, "<tt class="samp">assert expression1, expression2</tt>", is | |
| 90 | equivalent to | |
| 91 | ||
| 92 | <P> | |
| 93 | <div class="verbatim"><pre> | |
| 94 | if __debug__: | |
| 95 | if not expression1: raise AssertionError, expression2 | |
| 96 | </pre></div> | |
| 97 | ||
| 98 | <P> | |
| 99 | These equivalences assume that <code>__debug__</code><a id='l2h-464' xml:id='l2h-464'></a> and | |
| 100 | <tt class="exception">AssertionError</tt><a id='l2h-463' xml:id='l2h-463'></a> refer to the built-in | |
| 101 | variables with those names. In the current implementation, the | |
| 102 | built-in variable <code>__debug__</code> is <code>True</code> under normal | |
| 103 | circumstances, <code>False</code> when optimization is requested (command line | |
| 104 | option -O). The current code generator emits no code for an assert | |
| 105 | statement when optimization is requested at compile time. Note that it | |
| 106 | is unnecessary to include the source code for the expression that failed | |
| 107 | in the error message; | |
| 108 | it will be displayed as part of the stack trace. | |
| 109 | ||
| 110 | <P> | |
| 111 | Assignments to <code>__debug__</code> are illegal. The value for the | |
| 112 | built-in variable is determined when the interpreter starts. | |
| 113 | ||
| 114 | <P> | |
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