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<H3><A NAME="SECTION0082042000000000000000"><!--x--></A><A NAME="optparse-callbacks-called"><!--z--></A>
<BR>
6.20.4.2 How callbacks are called
</H3>
<P>
All callbacks are called as follows:
<P>
<div class="verbatim"><pre>
func(option, opt, value, parser, *args, **kwargs)
</pre></div>
<P>
where
<P>
<dl class="definitions">
<dt><b><a id='l2h-2028'>option</a></b></dt>
<dd>
is the <tt class="class">Option</tt> instance that's calling the callback.
<P>
<dt><b><a id='l2h-2029'>opt</a></b></dt>
<dd>
is the option string seen on the command-line that's triggering the
callback. (If an abbreviated long option was used, <var>opt</var> will be
the full, canonical option string--for example, if the user puts
<b class="programopt">--foo</b> on the command-line as an abbreviation for
<b class="programopt">--foobar</b>, then <var>opt</var> will be
<b class="programopt">--foobar</b>.)
<P>
<dt><b><a id='l2h-2030'>value</a></b></dt>
<dd>
is the argument to this option seen on the command-line.
<tt class="module">optparse</tt> will only expect an argument if <var>type</var> is
set; the type of <var>value</var> will be the type implied by the
option's type (see <A href="optparse-option-types.html#optparse-option-types">6.20.3</A>, ``Option types''). If
<var>type</var> for this option is <code>None</code> (no argument expected), then
<var>value</var> will be <code>None</code>. If "<tt class="samp">nargs > 1</tt>", <var>value</var> will
be a tuple of values of the appropriate type.
<P>
<dt><b><a id='l2h-2031'>parser</a></b></dt>
<dd>
is the <tt class="class">OptionParser</tt> instance driving the whole thing, mainly
useful because you can access some other interesting data through it,
as instance attributes:
<P>
<dl class="definitions"><dt><b><a id='l2h-2032'>parser.rargs</a></b></dt>
<dd>
the current remaining argument list, i.e. with <var>opt</var> (and
<var>value</var>, if any) removed, and only the arguments following
them still there. Feel free to modify <tt class="member">parser.rargs</tt>,
e.g. by consuming more arguments.
<P>
<dt><b><a id='l2h-2033'>parser.largs</a></b></dt>
<dd>
the current set of leftover arguments, i.e. arguments that have been
processed but have not been consumed as options (or arguments to
options). Feel free to modify <tt class="member">parser.largs</tt> e.g. by adding
more arguments to it.
<P>
<dt><b><a id='l2h-2034'>parser.values</a></b></dt>
<dd>
the object where option values are by default stored. This is useful
because it lets callbacks use the same mechanism as the rest of
<tt class="module">optparse</tt> for storing option values; you don't need to mess
around with globals or closures. You can also access the value(s) of
any options already encountered on the command-line.
</dl>
<P>
<dt><b><a id='l2h-2035'>args</a></b></dt>
<dd>
is a tuple of arbitrary positional arguments supplied via the
<var>callback</var>_args option attribute.
<P>
<dt><b><a id='l2h-2036'>kwargs</a></b></dt>
<dd>
is a dictionary of arbitrary keyword arguments supplied via
<var>callback_kwargs</var>.
</dl>
<P>
Since <var>args</var> and <var>kwargs</var> are optional (they are only passed
if you supply <var>callback_args</var> and/or <var>callback_kwargs</var> when
you define your callback option), the minimal callback function is:
<P>
<div class="verbatim"><pre>
def my_callback (option, opt, value, parser):
pass
</pre></div>
<P>
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<span class="release-info">Release 2.3.4, documentation updated on May 20, 2004.</span>
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