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<title>6.9 The raise statement </title>
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<H1><A NAME="SECTION008900000000000000000"></A><A NAME="raise"></A>
<BR>
6.9 The <tt class="keyword">raise</tt> statement
</H1>
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    <td><a id='tok-raise_stmt' xml:id='tok-raise_stmt'>raise_stmt</a></td>
    <td>::=</td>
    <td>"raise" [<a class='grammartoken' href="Booleans.html#tok-expression">expression</a> ["," <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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<P>
If no expressions are present, <tt class="keyword">raise</tt> re-raises the last
exception that was active in the current scope.  If no exception is
active in the current scope, a <tt class="exception">Queue.Empty</tt> exception is
raised indicating this error.
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<a id='l2h-514' xml:id='l2h-514'></a>
<P>
Otherwise, <tt class="keyword">raise</tt> evaluates the expressions to get three
objects, using <code>None</code> as the value of omitted expressions.  The
first two objects are used to determine the <em>type</em> and
<em>value</em> of the exception.

<P>
If the first object is an instance, the type of the exception is the
class of the instance, the instance itself is the value, and the
second object must be <code>None</code>.

<P>
If the first object is a class, it becomes the type of the exception.
The second object is used to determine the exception value: If it is
an instance of the class, the instance becomes the exception value.
If the second object is a tuple, it is used as the argument list for
the class constructor; if it is <code>None</code>, an empty argument list is
used, and any other object is treated as a single argument to the
constructor.  The instance so created by calling the constructor is
used as the exception value.

<P>
If a third object is present and not <code>None</code>, it must be a
traceback<a id='l2h-515' xml:id='l2h-515'></a> object (see section&nbsp;<A href="types.html#traceback">3.2</A>), and
it is substituted instead of the current location as the place where
the exception occurred.  If the third object is present and not a
traceback object or <code>None</code>, a <tt class="exception">TypeError</tt> exception is
raised.  The three-expression form of <tt class="keyword">raise</tt> is useful to
re-raise an exception transparently in an except clause, but
<tt class="keyword">raise</tt> with no expressions should be preferred if the
exception to be re-raised was the most recently active exception in
the current scope.

<P>
Additional information on exceptions can be found in
section&nbsp;<A href="exceptions.html#exceptions">4.2</A>, and information about handling exceptions is
in section&nbsp;<A href="try.html#try">7.4</A>.

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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