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<title>6.21.3.5 Option attributes</title>
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<H3><A NAME="SECTION0082135000000000000000"></A><A NAME="optparse-option-attributes"></A>
<BR>
6.21.3.5 Option attributes
</H3>
<P>
The following option attributes may be passed as keyword arguments
to <code>parser.add_option()</code>. If you pass an option attribute
that is not relevant to a particular option, or fail to pass a required
option attribute, <tt class="module">optparse</tt> raises OptionError.
<UL>
<LI>
<tt class="member">action</tt> (default: <code>"store"</code>)
<P>
Determines <tt class="module">optparse</tt>'s behaviour when this option is seen on the command
line; the available options are documented above.
<P>
</LI>
<LI>
<tt class="member">type</tt> (default: <code>"string"</code>)
<P>
The argument type expected by this option (e.g., <code>"string"</code> or
<code>"int"</code>); the available option types are documented below.
<P>
</LI>
<LI>
<tt class="member">dest</tt> (default: derived from option strings)
<P>
If the option's action implies writing or modifying a value somewhere,
this tells <tt class="module">optparse</tt> where to write it: <tt class="member">dest</tt> names an attribute of the
<code>options</code> object that <tt class="module">optparse</tt> builds as it parses the command line.
<P>
</LI>
<LI>
<code>default</code> (deprecated)
<P>
The value to use for this option's destination if the option is not
seen on the command line. Deprecated; use <code>parser.set_defaults()</code>
instead.
<P>
</LI>
<LI>
<code>nargs</code> (default: 1)
<P>
How many arguments of type <tt class="member">type</tt> should be consumed when this
option is seen. If > 1, <tt class="module">optparse</tt> will store a tuple of values to
<tt class="member">dest</tt>.
<P>
</LI>
<LI>
<code>const</code>
<P>
For actions that store a constant value, the constant value to store.
<P>
</LI>
<LI>
<code>choices</code>
<P>
For options of type <code>"choice"</code>, the list of strings the user
may choose from.
<P>
</LI>
<LI>
<code>callback</code>
<P>
For options with action <code>"callback"</code>, the callable to call when this
option is seen. See section <A href="optparse-option-callbacks.html#optparse-option-callbacks">6.21.4</A>, Option Callbacks for detail on the arguments
passed to <code>callable</code>.
<P>
</LI>
<LI>
<code>callback_args</code>, <code>callback_kwargs</code>
<P>
Additional positional and keyword arguments to pass to <code>callback</code>
after the four standard callback arguments.
<P>
</LI>
<LI>
<tt class="member">help</tt>
<P>
Help text to print for this option when listing all available options
after the user supplies a <tt class="member">help</tt> option (such as <code>"-help"</code>).
If no help text is supplied, the option will be listed without help
text. To hide this option, use the special value <code>SUPPRESS_HELP</code>.
<P>
</LI>
<LI>
<code>metavar</code> (default: derived from option strings)
<P>
Stand-in for the option argument(s) to use when printing help text.
See section <A href="optparse-tutorial.html#optparse-tutorial">6.21.2</A>, the tutorial for an example.
<P>
</LI>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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