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<H2><A NAME="SECTION0082120000000000000000"></A><A NAME="optparse-tutorial"></A>
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6.21.2 Tutorial
</H2>

<P>
While <tt class="module">optparse</tt> is quite flexible and powerful, it's also straightforward to
use in most cases.  This section covers the code patterns that are
common to any <tt class="module">optparse</tt>-based program.

<P>
First, you need to import the OptionParser class; then, early in the
main program, create an OptionParser instance:
<div class="verbatim"><pre>
from optparse import OptionParser
[...]
parser = OptionParser()
</pre></div>

<P>
Then you can start defining options.  The basic syntax is:
<div class="verbatim"><pre>
parser.add_option(opt_str, ...,
                  attr=value, ...)
</pre></div>

<P>
Each option has one or more option strings, such as <code>"-f"</code> or
<code>"-file"</code>, and several option attributes that tell <tt class="module">optparse</tt> what to
expect and what to do when it encounters that option on the command
line.

<P>
Typically, each option will have one short option string and one long
option string, e.g.:
<div class="verbatim"><pre>
parser.add_option("-f", "--file", ...)
</pre></div>

<P>
You're free to define as many short option strings and as many long
option strings as you like (including zero), as long as there is at
least one option string overall.

<P>
The option strings passed to <tt class="method">add_option()</tt> are effectively labels for
the option defined by that call.  For brevity, we will frequently refer
to <em>encountering an option</em> on the command line; in reality, <tt class="module">optparse</tt>
encounters <em>option strings</em> and looks up options from them.

<P>
Once all of your options are defined, instruct <tt class="module">optparse</tt> to parse your
program's command line:
<div class="verbatim"><pre>
(options, args) = parser.parse_args()
</pre></div>

<P>
(If you like, you can pass a custom argument list to <tt class="method">parse_args()</tt>,
but that's rarely necessary: by default it uses <code>sys.argv[1:]</code>.)

<P>
<tt class="method">parse_args()</tt> returns two values:

<UL>
<LI>
<code>options</code>, an object containing values for all of your options--e.g. if <code>"-file"</code> takes a single string argument, then
<code>options.file</code> will be the filename supplied by the user, or
<code>None</code> if the user did not supply that option

<P>
</LI>
<LI>
<code>args</code>, the list of positional arguments leftover after parsing
options

<P>
</LI>
</UL>

<P>
This tutorial section only covers the four most important option
attributes: <tt class="member">action</tt>, <tt class="member">type</tt>, <tt class="member">dest</tt> (destination), and <tt class="member">help</tt>.
Of these, <tt class="member">action</tt> is the most fundamental.

<P>

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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>

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<LI><A href="optparse-understanding-option-actions.html">6.21.2.1 Understanding option actions</a>
<LI><A href="optparse-store-action.html">6.21.2.2 The store action</a>
<LI><A href="optparse-handling-boolean-options.html">6.21.2.3 Handling boolean (flag) options</a>
<LI><A href="optparse-other-actions.html">6.21.2.4 Other actions</a>
<LI><A href="optparse-default-values.html">6.21.2.5 Default values</a>
<LI><A href="optparse-generating-help.html">6.21.2.6 Generating help</a>
<LI><A href="optparse-printing-version-string.html">6.21.2.7 Printing a version string</a>
<LI><A href="optparse-how-optparse-handles-errors.html">6.21.2.8 How <tt class="module">optparse</tt> handles errors</a>
<LI><A href="optparse-putting-it-all-together.html">6.21.2.9 Putting it all together</a>
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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