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<title>6.14 The exec statement
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<H1><A NAME=
"SECTION0081400000000000000000"></A><A NAME=
"exec"></A>
6.14 The
<tt class=
"keyword">exec
</tt> statement
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<div class=
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<td><a id='tok-exec_stmt' xml:id='tok-exec_stmt'
>exec_stmt
</a></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>]]
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<a class=
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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
<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.
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>
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-
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<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=
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2.4.2, documentation updated on
28 September
2005.
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