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<h2 style="text-align: left;">Handling libtrace errors</h2><big><span style="font-weight: bold;">Exception plt_exc_libtrace</span></big><br /><br /><span style="font-style: italic;">plt_libtrace_exc </span> is a subclass of Python's <span style="font-style: italic;">SystemError</span> exception. Python-libtrace checks for errors during operations on traces, see the <span style="font-style: italic;">Trace</span> and <span style="font-style: italic;">OutputTrace</span> page for further information.<br /><br />For most purposes you can simply invoke the <span style="font-style: italic;">Trace</span> and <span style="font-style: italic;">OutputTrace</span> methods, knowing that if python-libtrace encounters an error it will throw a <span style="font-style: italic;">LibtraceError</span> and <span style="font-style: italic;">exit</span>, with the Python interpreter printing a diagnostic line to tell you what it thinks caused the problem.<br />Alternatively, you can catch the exception using a "try-except block," like this:
<br /><br /> <span style="font-style: italic;">try:</span><br style="font-style: italic;" /><span style="font-style: italic;"> f = plt.trace(ARGV[0])</span><br style="font-style: italic;" /><span style="font-style: italic;"> except:</span><br style="font-style: italic;" /><span style="font-style: italic;"> print "helpful message\n"</span><br style="font-style: italic;" /><span style="font-style: italic;"> sys.exc_clear()</span><br style="font-style: italic;" /><span style="font-style: italic;"><br /></span>Here, the <span style="font-style: italic;">sys.exc_clear() </span>statement simply clears the exception history.<p>Nevil Brownlee<br />Mon, 30 Jun 14 (NZST)</p>
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