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<table width="100%" cellpadding=5 cellspacing=0 border=0 class="navtopbg"><tr><td><font size="1"><p class="navtitle"><a href="8.html" class="navtitle">Web Development</a> > <a href="0672319942.html" class="navtitle">Python Developer's Handbook</a> > <a href="91.html" class="navtitle">4. Exception Handling</a> > <span class="nonavtitle">try/finally </span></p></font></td><td align="right" valign="top" nowrap><font size="1"><a href="main.asp?list" class="safnavoff">See All Titles</a></font></td></tr></table>
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<FONT><h3><tt cLASS="monofont"><a namE="idx1073743206"></A><A Name="idx1073743207"></a><A NAMe="idx1073743208"></a>try/finally</tt></h3>
<p>The <a name="idx1073743209"></a><a name="idx1073743210"></a><tt ClaSs="monofont">try/finally</tt> statement is good for clean-up actions. The code in the <A name="idx1073743211"></A><a naME="idx1073743212"></A><Tt claSS="monofont">finally</TT> block is always executed, no matter whether the <tt clASS="monofont">try</Tt> block fails or not.</p>
<prE>
1: try:
2: f = open("c:\\autoexec.bat")
3: lines = f.readlines()
4: finally:
5: f.close() # it is always executed
6: print "It is done" # it is executed on success only
</PRE>
<p>The previous piece of code opens a file and tries to read its lines. It is not necessary to check whether the process raises an error in order to close the file because the <tt class="monofont">close</tt> function in line 5 is always executed, no matter what. Now, take a look at line 6. The <tt class="monofont">print</tt> statement is only executed when the <tT clAss="monofont">finally</tT> block is bypassed because when an error is raised, the <tt clAss="monofont">finally</tT> block is executed and the program is terminated immediately afterwards if the exception is not handled, leaving the exception unhandled.</P>
<DIv claSS="note"><P Class="notetitle"><B>Tip</B></P><P>
<p><tt cLASS="monofont">finally</tt> and <a name="idx1073743213"></a><a name="idx1073743214"></a><tt clasS="monofont">except</tt> clauses cannot be used together along with a unique <A namE="idx1073743215"></a><a naMe="idx1073743216"></a><tT CLAss="monofont">try</tt> clause.<A NAMe="idx1073743217"></a><a nAME="idx1073743218"></A><a namE="idx1073743219"></A><A Name="idx1073743220"></a><a name="idx1073743221"></a></p>
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<P><TABLE width="100%" border=0><TR valign="top"><TD><font size=1 color="#C0C0C0"><br></font></TD><TD align=right><font size=1 color="#C0C0C0">Last updated on 1/30/2002<br>Python Developer's Handbook, © 2002 Sams Publishing</font></TD></TR></TABLE></P>
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<br><TABLE width=100% bgcolor=white border=0 cellspacing=0 cellpadding=5><TR><TD><H4 class=Title>Index terms contained in this section</H4>
<font size=2>
clauses<BR>
<a href="#idx1073743214">except</a><BR>
<a href="#idx1073743212">finally</a> <a href="#idx1073743221">2nd</a><BR>
<a href="#idx1073743216">try</a><BR>
<a href="#idx1073743213">except clause</a><BR>
exceptions<BR>
<a href="#idx1073743206">try/finally statement</a> <a href="#idx1073743217">2nd</a><BR>
<a href="#idx1073743211">finally clause</a> <a href="#idx1073743220">2nd</a><BR>
statements<BR>
<a href="#idx1073743207">try/finally</a> <a href="#idx1073743210">2nd</a> <a href="#idx1073743218">3rd</a><BR>
<a href="#idx1073743215">try clause</a><BR>
<a href="#idx1073743208">try/finally statement</a> <a href="#idx1073743209">2nd</a> <a href="#idx1073743219">3rd</a><BR>
<BR>
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