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<title>6.21.3.1 Creating the parser</title>
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<H3><A NAME="SECTION0082131000000000000000"></A><A NAME="optparse-creating-parser"></A>
<BR>
6.21.3.1 Creating the parser
</H3>

<P>
The first step in using <tt class="module">optparse</tt> is to create an OptionParser instance:
<div class="verbatim"><pre>
parser = OptionParser(...)
</pre></div>

<P>
The OptionParser constructor has no required arguments, but a number of
optional keyword arguments.  You should always pass them as keyword
arguments, i.e. do not rely on the order in which the arguments are
declared.
<BLOCKQUOTE>
</BLOCKQUOTE><DL>
<DT><STRONG><code>usage</code> (default: <code>"%prog [options]"</code>)</STRONG></DT>
<DD>The usage summary to print when your program is run incorrectly or
with a help option.  When <tt class="module">optparse</tt> prints the usage string, it expands
<code>%prog</code> to <code>os.path.basename(sys.argv[0])</code> (or to <code>prog</code> if
you passed that keyword argument).  To suppress a usage message,
pass the special value <code>optparse.SUPPRESS_USAGE</code>.
</DD>
<DT><STRONG><code>option_list</code> (default: <code>[]</code>)</STRONG></DT>
<DD>A list of Option objects to populate the parser with.  The options
in <code>option_list</code> are added after any options in
<code>standard_option_list</code> (a class attribute that may be set by
OptionParser subclasses), but before any version or help options.
Deprecated; use <tt class="method">add_option()</tt> after creating the parser instead.
</DD>
<DT><STRONG><code>option_class</code> (default: optparse.Option)</STRONG></DT>
<DD>Class to use when adding options to the parser in <tt class="method">add_option()</tt>.
</DD>
<DT><STRONG><code>version</code> (default: <code>None</code>)</STRONG></DT>
<DD>A version string to print when the user supplies a version option.
If you supply a true value for <code>version</code>, <tt class="module">optparse</tt> automatically adds
a version option with the single option string <code>"-version"</code>.  The
substring <code>"%prog"</code> is expanded the same as for <code>usage</code>.
</DD>
<DT><STRONG><code>conflict_handler</code> (default: <code>"error"</code>)</STRONG></DT>
<DD>Specifies what to do when options with conflicting option strings
are added to the parser; see section&nbsp;<A href="optparse-conflicts-between-options.html#optparse-conflicts-between-options">6.21.3</A>, Conflicts between options.
</DD>
<DT><STRONG><code>description</code> (default: <code>None</code>)</STRONG></DT>
<DD>A paragraph of text giving a brief overview of your program.  <tt class="module">optparse</tt>
reformats this paragraph to fit the current terminal width and
prints it when the user requests help (after <code>usage</code>, but before
the list of options).
</DD>
<DT><STRONG><code>formatter</code> (default: a new IndentedHelpFormatter)</STRONG></DT>
<DD>An instance of optparse.HelpFormatter that will be used for
printing help text.  <tt class="module">optparse</tt> provides two concrete classes for this
purpose: IndentedHelpFormatter and TitledHelpFormatter.
</DD>
<DT><STRONG><code>add_help_option</code> (default: <code>True</code>)</STRONG></DT>
<DD>If true, <tt class="module">optparse</tt> will add a help option (with option strings <code>"-h"</code>
and <code>"-help"</code>) to the parser.
</DD>
<DT><STRONG><code>prog</code></STRONG></DT>
<DD>The string to use when expanding <code>"%prog"</code> in <code>usage</code> and
<code>version</code> instead of <code>os.path.basename(sys.argv[0])</code>.
</DD>
</DL><BLOCKQUOTE>
</BLOCKQUOTE>

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