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<H3><A NAME="SECTION0082153000000000000000"></A><A NAME="optparse-other-reasons-to-extend-optparse"></A>
<BR>
6.21.5.3 Other reasons to extend <tt class="module">optparse</tt>
</H3>

<P>
Adding new types and new actions are the big, obvious reasons why you
might want to extend <tt class="module">optparse</tt>.  I can think of at least two other areas to
play with.

<P>
First, the simple one: OptionParser tries to be helpful by calling
<tt class="function">sys.exit()</tt> when appropriate, i.e. when there's an error on the
command line or when the user requests help.  In the former case, the
traditional course of letting the script crash with a traceback is
unacceptable; it will make users think there's a bug in your script when
they make a command-line error.  In the latter case, there's generally
not much point in carrying on after printing a help message.

<P>
If this behaviour bothers you, it shouldn't be too hard to ``fix'' it.
You'll have to

<DL COMPACT>
<DT>

1)
<DD>
subclass OptionParser and override <tt class="method">error()</tt>

<P>
<DT>

2)
<DD>
subclass Option and override <tt class="method">take_action()</tt>--you'll
need to provide your own handling of the <tt class="member">help</tt> action that
doesn't call <tt class="function">sys.exit()</tt>

<P>
</DD>
</DL>

<P>
The second, much more complex, possibility is to override the
command-line syntax implemented by <tt class="module">optparse</tt>.  In this case, you'd leave the
whole machinery of option actions and types alone, but rewrite the code
that processes <var>sys.argv</var>.  You'll need to subclass OptionParser in any
case; depending on how radical a rewrite you want, you'll probably need
to override one or all of <tt class="method">parse_args()</tt>, <tt class="method">_process_long_opt()</tt>, and
<tt class="method">_process_short_opts()</tt>.

<P>
Both of these are left as an exercise for the reader.  I have not tried
to implement either myself, since I'm quite happy with <tt class="module">optparse</tt>'s default
behaviour (naturally).

<P>
Happy hacking, and don't forget: Use the Source, Luke.

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