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<H3><A NAME="SECTION0082134000000000000000"></A><A NAME="optparse-standard-option-actions"></A>
<BR>
6.21.3.4 Standard option actions
</H3>

<P>
The various option actions all have slightly different requirements and
effects.  Most actions have several relevant option attributes which you
may specify to guide <tt class="module">optparse</tt>'s behaviour; a few have required attributes,
which you must specify for any option using that action.

<UL>
<LI>
<code>store</code> [relevant: <tt class="member">type</tt>, <tt class="member">dest</tt>, <code>nargs</code>, <code>choices</code>]

<P>
The option must be followed by an argument, which is
converted to a value according to <tt class="member">type</tt> and stored in
<tt class="member">dest</tt>.  If <code>nargs</code> &gt; 1, multiple arguments will be consumed
from the command line; all will be converted according to
<tt class="member">type</tt> and stored to <tt class="member">dest</tt> as a tuple.  See the ``Option
types'' section below.

<P>
If <code>choices</code> is supplied (a list or tuple of strings), the type
defaults to <code>choice</code>.

<P>
If <tt class="member">type</tt> is not supplied, it defaults to <code>string</code>.

<P>
If <tt class="member">dest</tt> is not supplied, <tt class="module">optparse</tt> derives a destination from the
first long option string (e.g., <code>"-foo-bar"</code> implies <code>foo_bar</code>).
If there are no long option strings, <tt class="module">optparse</tt> derives a destination from
the first short option string (e.g., <code>"-f"</code> implies <code>f</code>).

<P>
Example:
<div class="verbatim"><pre>
parser.add_option("-f")
parser.add_option("-p", type="float", nargs=3, dest="point")
</pre></div>

<P>
As it parses the command line
<div class="verbatim"><pre>
-f foo.txt -p 1 -3.5 4 -fbar.txt
</pre></div>

<P>
<tt class="module">optparse</tt> will set
<div class="verbatim"><pre>
options.f = "foo.txt"
options.point = (1.0, -3.5, 4.0)
options.f = "bar.txt"
</pre></div>

<P>
</LI>
<LI>
<code>store_const</code> [required: <code>const</code>; relevant: <tt class="member">dest</tt>]

<P>
The value <code>const</code> is stored in <tt class="member">dest</tt>.

<P>
Example:
<div class="verbatim"><pre>
parser.add_option("-q", "--quiet",
                  action="store_const", const=0, dest="verbose")
parser.add_option("-v", "--verbose",
                  action="store_const", const=1, dest="verbose")
parser.add_option("--noisy",
                  action="store_const", const=2, dest="verbose")
</pre></div>

<P>
If <code>"-noisy"</code> is seen, <tt class="module">optparse</tt> will set
<div class="verbatim"><pre>
options.verbose = 2
</pre></div>

<P>
</LI>
<LI>
<code>store_true</code> [relevant: <tt class="member">dest</tt>]

<P>
A special case of <code>store_const</code> that stores a true value
to <tt class="member">dest</tt>.

<P>
</LI>
<LI>
<code>store_false</code> [relevant: <tt class="member">dest</tt>]

<P>
Like <code>store_true</code>, but stores a false value.

<P>
Example:
<div class="verbatim"><pre>
parser.add_option("--clobber", action="store_true", dest="clobber")
parser.add_option("--no-clobber", action="store_false", dest="clobber")
</pre></div>

<P>
</LI>
<LI>
<code>append</code> [relevant: <tt class="member">type</tt>, <tt class="member">dest</tt>, <code>nargs</code>, <code>choices</code>]

<P>
The option must be followed by an argument, which is appended to the
list in <tt class="member">dest</tt>.  If no default value for <tt class="member">dest</tt> is supplied, an
empty list is automatically created when <tt class="module">optparse</tt> first encounters this
option on the command-line.  If <code>nargs</code> &gt; 1, multiple arguments are
consumed, and a tuple of length <code>nargs</code> is appended to <tt class="member">dest</tt>.

<P>
The defaults for <tt class="member">type</tt> and <tt class="member">dest</tt> are the same as for the
<code>store</code> action.

<P>
Example:
<div class="verbatim"><pre>
parser.add_option("-t", "--tracks", action="append", type="int")
</pre></div>

<P>
If <code>"-t3"</code> is seen on the command-line, <tt class="module">optparse</tt> does the equivalent of:
<div class="verbatim"><pre>
options.tracks = []
options.tracks.append(int("3"))
</pre></div>

<P>
If, a little later on, <code>"-tracks=4"</code> is seen, it does:
<div class="verbatim"><pre>
options.tracks.append(int("4"))
</pre></div>

<P>
</LI>
<LI>
<code>count</code> [relevant: <tt class="member">dest</tt>]

<P>
Increment the integer stored at <tt class="member">dest</tt>.  If no default value is
supplied, <tt class="member">dest</tt> is set to zero before being incremented the first
time.

<P>
Example:
<div class="verbatim"><pre>
parser.add_option("-v", action="count", dest="verbosity")
</pre></div>

<P>
The first time <code>"-v"</code> is seen on the command line, <tt class="module">optparse</tt> does the
equivalent of:
<div class="verbatim"><pre>
options.verbosity = 0
options.verbosity += 1
</pre></div>

<P>
Every subsequent occurrence of <code>"-v"</code> results in
<div class="verbatim"><pre>
options.verbosity += 1
</pre></div>

<P>
</LI>
<LI>
<code>callback</code> [required: <code>callback</code>;
relevant: <tt class="member">type</tt>, <code>nargs</code>, <code>callback_args</code>, <code>callback_kwargs</code>]

<P>
Call the function specified by <code>callback</code>, which is called as
<div class="verbatim"><pre>
func(option, opt_str, value, parser, *args, **kwargs)
</pre></div>

<P>
See section&nbsp;<A href="optparse-option-callbacks.html#optparse-option-callbacks">6.21.4</A>, Option Callbacks for more detail.

<P>
</LI>
<LI>
<tt class="member">help</tt>

<P>
Prints a complete help message for all the options in the
current option parser.  The help message is constructed from
the <code>usage</code> string passed to OptionParser's constructor and
the <tt class="member">help</tt> string passed to every option.

<P>
If no <tt class="member">help</tt> string is supplied for an option, it will still be
listed in the help message.  To omit an option entirely, use
the special value <code>optparse.SUPPRESS_HELP</code>.

<P>
<tt class="module">optparse</tt> automatically adds a <tt class="member">help</tt> option to all OptionParsers, so
you do not normally need to create one.

<P>
Example:
<div class="verbatim"><pre>
from optparse import OptionParser, SUPPRESS_HELP

parser = OptionParser()
parser.add_option("-h", "--help", action="help"),
parser.add_option("-v", action="store_true", dest="verbose",
                  help="Be moderately verbose")
parser.add_option("--file", dest="filename",
                  help="Input file to read data from"),
parser.add_option("--secret", help=SUPPRESS_HELP)
</pre></div>

<P>
If <tt class="module">optparse</tt> sees either <code>"-h"</code> or <code>"-help"</code> on the command line, it
will print something like the following help message to stdout
(assuming <code>sys.argv[0]</code> is <code>"foo.py"</code>):
<div class="verbatim"><pre>
usage: foo.py [options]

options:
  -h, --help        Show this help message and exit
  -v                Be moderately verbose
  --file=FILENAME   Input file to read data from
</pre></div>

<P>
After printing the help message, <tt class="module">optparse</tt> terminates your process
with <code>sys.exit(0)</code>.

<P>
</LI>
<LI>
<code>version</code>

<P>
Prints the version number supplied to the OptionParser to stdout and
exits.  The version number is actually formatted and printed by the
<code>print_version()</code> method of OptionParser.  Generally only relevant
if the <code>version</code> argument is supplied to the OptionParser
constructor.  As with <tt class="member">help</tt> options, you will rarely create
<code>version</code> options, since <tt class="module">optparse</tt> automatically adds them when needed.

<P>
</LI>
</UL>

<P>

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