MOON
Server: Apache/2.2.31 (Unix) mod_ssl/2.2.31 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4
System: Linux csr818.wilogic.com 2.6.18-419.el5xen #1 SMP Fri Feb 24 22:50:37 UTC 2017 x86_64
User: digitals (531)
PHP: 5.4.45
Disabled: NONE
$ pwd: /usr/share/doc/python-docs-2.4.3/html/lib/
Upload Files
File: //usr/share/doc/python-docs-2.4.3/html/lib/optparse-defining-options.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="optparse-standard-option-actions.html" />
<link rel="prev" href="optparse-populating-parser.html" />
<link rel="parent" href="optparse-reference-guide.html" />
<link rel="next" href="optparse-standard-option-actions.html" />
<meta name='aesop' content='information' />
<title>6.21.3.3 Defining options</title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="6.21.3.2 Populating the parser"
  href="optparse-populating-parser.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="6.21.3 Reference Guide"
  href="optparse-reference-guide.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="6.21.3.4 Standard option actions"
  href="optparse-standard-option-actions.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="optparse-populating-parser.html">6.21.3.2 Populating the parser</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="optparse-reference-guide.html">6.21.3 Reference Guide</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="optparse-standard-option-actions.html">6.21.3.4 Standard option actions</A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H3><A NAME="SECTION0082133000000000000000"></A><A NAME="optparse-defining-options"></A>
<BR>
6.21.3.3 Defining options
</H3>

<P>
Each Option instance represents a set of synonymous command-line option
strings, e.g. <b class="programopt">-f</b> and <b class="programopt">--file</b>.  You can
specify any number of short or long option strings, but you must specify
at least one overall option string.

<P>
The canonical way to create an Option instance is with the
<tt class="method">add_option()</tt> method of <tt class="class">OptionParser</tt>:
<div class="verbatim"><pre>
parser.add_option(opt_str[, ...], attr=value, ...)
</pre></div>

<P>
To define an option with only a short option string:
<div class="verbatim"><pre>
parser.add_option("-f", attr=value, ...)
</pre></div>

<P>
And to define an option with only a long option string:
<div class="verbatim"><pre>
parser.add_option("--foo", attr=value, ...)
</pre></div>

<P>
The keyword arguments define attributes of the new Option object.  The
most important option attribute is <tt class="member">action</tt>, and it largely determines
which other attributes are relevant or required.  If you pass irrelevant
option attributes, or fail to pass required ones, <tt class="module">optparse</tt> raises an
OptionError exception explaining your mistake.

<P>
An options's <em>action</em> determines what <tt class="module">optparse</tt> does when it encounters this
option on the command-line.  The standard option actions hard-coded into
<tt class="module">optparse</tt> are:
<DL>
<DT><STRONG><code>store</code></STRONG></DT>
<DD>store this option's argument (default)
</DD>
<DT><STRONG><code>store_const</code></STRONG></DT>
<DD>store a constant value
</DD>
<DT><STRONG><code>store_true</code></STRONG></DT>
<DD>store a true value
</DD>
<DT><STRONG><code>store_false</code></STRONG></DT>
<DD>store a false value
</DD>
<DT><STRONG><code>append</code></STRONG></DT>
<DD>append this option's argument to a list
</DD>
<DT><STRONG><code>count</code></STRONG></DT>
<DD>increment a counter by one
</DD>
<DT><STRONG><code>callback</code></STRONG></DT>
<DD>call a specified function
</DD>
<DT><STRONG><tt class="member">help</tt></STRONG></DT>
<DD>print a usage message including all options and the
documentation for them
</DD>
</DL>

<P>
(If you don't supply an action, the default is <code>store</code>.  For this
action, you may also supply <tt class="member">type</tt> and <tt class="member">dest</tt> option attributes; see
below.)

<P>
As you can see, most actions involve storing or updating a value
somewhere.  <tt class="module">optparse</tt> always creates a special object for this,
conventionally called <code>options</code> (it happens to be an instance of
<code>optparse.Values</code>).  Option arguments (and various other values) are
stored as attributes of this object, according to the <tt class="member">dest</tt>
(destination) option attribute.

<P>
For example, when you call
<div class="verbatim"><pre>
parser.parse_args()
</pre></div>

<P>
one of the first things <tt class="module">optparse</tt> does is create the <code>options</code> object:
<div class="verbatim"><pre>
options = Values()
</pre></div>

<P>
If one of the options in this parser is defined with
<div class="verbatim"><pre>
parser.add_option("-f", "--file", action="store", type="string", dest="filename")
</pre></div>

<P>
and the command-line being parsed includes any of the following:
<div class="verbatim"><pre>
-ffoo
-f foo
--file=foo
--file foo
</pre></div>

<P>
then <tt class="module">optparse</tt>, on seeing this option, will do the equivalent of
<div class="verbatim"><pre>
options.filename = "foo"
</pre></div>

<P>
The <tt class="member">type</tt> and <tt class="member">dest</tt> option attributes are almost as important as
<tt class="member">action</tt>, but <tt class="member">action</tt> is the only one that makes sense for <em>all</em>
options.

<P>

<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="6.21.3.2 Populating the parser"
  href="optparse-populating-parser.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="6.21.3 Reference Guide"
  href="optparse-reference-guide.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="6.21.3.4 Standard option actions"
  href="optparse-standard-option-actions.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="optparse-populating-parser.html">6.21.3.2 Populating the parser</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="optparse-reference-guide.html">6.21.3 Reference Guide</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="optparse-standard-option-actions.html">6.21.3.4 Standard option actions</A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>
@ Telegram