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<title>6.14 The exec statement </title>
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<H1><A NAME="SECTION0081400000000000000000"></A><A NAME="exec"></A>
<BR>
6.14 The <tt class="keyword">exec</tt> statement
</H1>
<a id='l2h-563' xml:id='l2h-563'></a>
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    <td><a id='tok-exec_stmt' xml:id='tok-exec_stmt'>exec_stmt</a></td>
    <td>::=</td>
    <td>"exec" <a class='grammartoken' href="Booleans.html#tok-expression">expression</a>
              ["in" <a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ["," <a class='grammartoken' href="Booleans.html#tok-expression">expression</a>]]</td></tr>
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<a class="grammar-footer"
  href="grammar.txt" type="text/plain"
  >Download entire grammar as text.</a>
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<P>
This statement supports dynamic execution of Python code.  The first
expression should evaluate to either a string, an open file object, or
a code object.  If it is a string, the string is parsed as a suite of
Python statements which is then executed (unless a syntax error
occurs).  If it is an open file, the file is parsed until EOF and
executed.  If it is a code object, it is simply executed.  In all
cases, the code that's executed is expected to be be valid as file
input (see section&nbsp;<A href="file-input.html#file-input">8.2</A>, ``File input'').  Be aware that
the <tt class="keyword">return</tt> and <tt class="keyword">yield</tt> statements may not be used
outside of function definitions even within the context of code passed
to the <tt class="keyword">exec</tt> statement.

<P>
In all cases, if the optional parts are omitted, the code is executed
in the current scope.  If only the first expression after <tt class="keyword">in</tt>
is specified, it should be a dictionary, which will be used for both
the global and the local variables.  If two expressions are given,
they are used for the global and local variables, respectively.
If provided, <var>locals</var> can be any mapping object.

<span class="versionnote">Changed in version 2.4:
formerly <var>locals</var> was required to be a dictionary.</span>

<P>
As a side effect, an implementation may insert additional keys into
the dictionaries given besides those corresponding to variable names
set by the executed code.  For example, the current implementation
may add a reference to the dictionary of the built-in module
<tt class="module">__builtin__</tt> under the key <code>__builtins__</code> (!).
<a id='l2h-567' xml:id='l2h-567'></a>

<P>
<strong>Programmer's hints:</strong>
dynamic evaluation of expressions is supported by the built-in
function <tt class="function">eval()</tt>.  The built-in functions
<tt class="function">globals()</tt> and <tt class="function">locals()</tt> return the current global
and local dictionary, respectively, which may be useful to pass around
for use by <tt class="keyword">exec</tt>.
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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