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| 54 | <H1><A NAME="SECTION0081400000000000000000"></A><A NAME="exec"></A> | |
| 55 | <BR> | |
| 56 | 6.14 The <tt class="keyword">exec</tt> statement | |
| 57 | </H1> | |
| 58 | <a id='l2h-563' xml:id='l2h-563'></a> | |
| 59 | <P> | |
| 60 | <dl><dd class="grammar"> | |
| 61 | <div class="productions"> | |
| 62 | <table> | |
| 63 | <tr> | |
| 64 | <td><a id='tok-exec_stmt' xml:id='tok-exec_stmt'>exec_stmt</a></td> | |
| 65 | <td>::=</td> | |
| 66 | <td>"exec" <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> | |
| 67 | ["in" <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ["," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a>]]</td></tr> | |
| 68 | </table> | |
| 69 | </div> | |
| 70 | <a class="grammar-footer" | |
| 71 | href="grammar.txt" type="text/plain" | |
| 72 | >Download entire grammar as text.</a> | |
| 73 | </dd></dl> | |
| 74 | ||
| 75 | <P> | |
| 76 | This statement supports dynamic execution of Python code. The first | |
| 77 | expression should evaluate to either a string, an open file object, or | |
| 78 | a code object. If it is a string, the string is parsed as a suite of | |
| 79 | Python statements which is then executed (unless a syntax error | |
| 80 | occurs). If it is an open file, the file is parsed until EOF and | |
| 81 | executed. If it is a code object, it is simply executed. In all | |
| 82 | cases, the code that's executed is expected to be be valid as file | |
| 83 | input (see section <A href="file-input.html#file-input">8.2</A>, ``File input''). Be aware that | |
| 84 | the <tt class="keyword">return</tt> and <tt class="keyword">yield</tt> statements may not be used | |
| 85 | outside of function definitions even within the context of code passed | |
| 86 | to the <tt class="keyword">exec</tt> statement. | |
| 87 | ||
| 88 | <P> | |
| 89 | In all cases, if the optional parts are omitted, the code is executed | |
| 90 | in the current scope. If only the first expression after <tt class="keyword">in</tt> | |
| 91 | is specified, it should be a dictionary, which will be used for both | |
| 92 | the global and the local variables. If two expressions are given, | |
| 93 | they are used for the global and local variables, respectively. | |
| 94 | If provided, <var>locals</var> can be any mapping object. | |
| 95 | ||
| 96 | <span class="versionnote">Changed in version 2.4: | |
| 97 | formerly <var>locals</var> was required to be a dictionary.</span> | |
| 98 | ||
| 99 | <P> | |
| 100 | As a side effect, an implementation may insert additional keys into | |
| 101 | the dictionaries given besides those corresponding to variable names | |
| 102 | set by the executed code. For example, the current implementation | |
| 103 | may add a reference to the dictionary of the built-in module | |
| 104 | <tt class="module">__builtin__</tt> under the key <code>__builtins__</code> (!). | |
| 105 | <a id='l2h-567' xml:id='l2h-567'></a> | |
| 106 | ||
| 107 | <P> | |
| 108 | <strong>Programmer's hints:</strong> | |
| 109 | dynamic evaluation of expressions is supported by the built-in | |
| 110 | function <tt class="function">eval()</tt>. The built-in functions | |
| 111 | <tt class="function">globals()</tt> and <tt class="function">locals()</tt> return the current global | |
| 112 | and local dictionary, respectively, which may be useful to pass around | |
| 113 | for use by <tt class="keyword">exec</tt>. | |
| 114 | <a id='l2h-564' xml:id='l2h-564'></a><a id='l2h-565' xml:id='l2h-565'></a><a id='l2h-566' xml:id='l2h-566'></a> | |
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| 151 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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