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<title>3.20.1 Warning Categories </title>
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<H2><A NAME="SECTION0052010000000000000000"></A><A NAME="warning-categories"></A>
<BR>
3.20.1 Warning Categories
</H2>

<P>
There are a number of built-in exceptions that represent warning
categories.  This categorization is useful to be able to filter out
groups of warnings.  The following warnings category classes are
currently defined:

<P>
<div class="center"><table class="realtable">
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    <tr>
      <th class="left"  >Class</th>
      <th class="left"  >Description</th>
      </tr>
    </thead>
  <tbody>
<P>

    <tr><td class="left"   valign="baseline"><tt class="exception">Warning</tt></td>
        <td class="left"  >This is the base class of all warning category
classes.  It is a subclass of <tt class="exception">Exception</tt>.</td></tr><P>

    <tr><td class="left"   valign="baseline"><tt class="exception">UserWarning</tt></td>
        <td class="left"  >The default category for <tt class="function">warn()</tt>.</td></tr><P>

    <tr><td class="left"   valign="baseline"><tt class="exception">DeprecationWarning</tt></td>
        <td class="left"  >Base category for warnings about
deprecated features.</td></tr><P>

    <tr><td class="left"   valign="baseline"><tt class="exception">SyntaxWarning</tt></td>
        <td class="left"  >Base category for warnings about dubious
syntactic features.</td></tr><P>

    <tr><td class="left"   valign="baseline"><tt class="exception">RuntimeWarning</tt></td>
        <td class="left"  >Base category for warnings about dubious
runtime features.</td></tr><P>

    <tr><td class="left"   valign="baseline"><tt class="exception">FutureWarning</tt></td>
        <td class="left"  >Base category for warnings about constructs
that will change semantically in the future.</td></tr><P>

    </tbody>
</table></div>

<P>
While these are technically built-in exceptions, they are documented
here, because conceptually they belong to the warnings mechanism.

<P>
User code can define additional warning categories by subclassing one
of the standard warning categories.  A warning category must always be
a subclass of the <tt class="exception">Warning</tt> class.

<P>

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