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<div class="section" id="module-getopt">
<span id="getopt-c-style-parser-for-command-line-options"></span><h1>15.6. <a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-mod docutils literal"><span class="pre">getopt</span></tt></a> — C-style parser for command line options<a class="headerlink" href="#module-getopt" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/3.2/Lib/getopt.py">Lib/getopt.py</a></p>
<hr class="docutils" />
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-mod docutils literal"><span class="pre">getopt</span></tt></a> module is a parser for command line options whose API is
designed to be familiar to users of the C <tt class="xref c c-func docutils literal"><span class="pre">getopt()</span></tt> function. Users who
are unfamiliar with the C <tt class="xref c c-func docutils literal"><span class="pre">getopt()</span></tt> function or who would like to write
less code and get better help and error messages should consider using the
<a class="reference internal" href="argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><tt class="xref py py-mod docutils literal"><span class="pre">argparse</span></tt></a> module instead.</p>
</div>
<p>This module helps scripts to parse the command line arguments in <tt class="docutils literal"><span class="pre">sys.argv</span></tt>.
It supports the same conventions as the Unix <tt class="xref c c-func docutils literal"><span class="pre">getopt()</span></tt> function (including
the special meanings of arguments of the form ‘<tt class="docutils literal"><span class="pre">-</span></tt>‘ and ‘<tt class="docutils literal"><span class="pre">--</span></tt>‘). Long
options similar to those supported by GNU software may be used as well via an
optional third argument.</p>
<p>This module provides two functions and an
exception:</p>
<dl class="function">
<dt id="getopt.getopt">
<tt class="descclassname">getopt.</tt><tt class="descname">getopt</tt><big>(</big><em>args</em>, <em>shortopts</em>, <em>longopts=</em><span class="optional">[</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#getopt.getopt" title="Permalink to this definition">¶</a></dt>
<dd><p>Parses command line options and parameter list. <em>args</em> is the argument list to
be parsed, without the leading reference to the running program. Typically, this
means <tt class="docutils literal"><span class="pre">sys.argv[1:]</span></tt>. <em>shortopts</em> is the string of option letters that the
script wants to recognize, with options that require an argument followed by a
colon (<tt class="docutils literal"><span class="pre">':'</span></tt>; i.e., the same format that Unix <tt class="xref c c-func docutils literal"><span class="pre">getopt()</span></tt> uses).</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Unlike GNU <tt class="xref c c-func docutils literal"><span class="pre">getopt()</span></tt>, after a non-option argument, all further
arguments are considered also non-options. This is similar to the way
non-GNU Unix systems work.</p>
</div>
<p><em>longopts</em>, if specified, must be a list of strings with the names of the
long options which should be supported. The leading <tt class="docutils literal"><span class="pre">'--'</span></tt> characters
should not be included in the option name. Long options which require an
argument should be followed by an equal sign (<tt class="docutils literal"><span class="pre">'='</span></tt>). Optional arguments
are not supported. To accept only long options, <em>shortopts</em> should be an
empty string. Long options on the command line can be recognized so long as
they provide a prefix of the option name that matches exactly one of the
accepted options. For example, if <em>longopts</em> is <tt class="docutils literal"><span class="pre">['foo',</span> <span class="pre">'frob']</span></tt>, the
option <tt class="docutils literal"><span class="pre">--fo</span></tt> will match as <tt class="docutils literal"><span class="pre">--foo</span></tt>, but <tt class="docutils literal"><span class="pre">--f</span></tt> will
not match uniquely, so <a class="reference internal" href="#getopt.GetoptError" title="getopt.GetoptError"><tt class="xref py py-exc docutils literal"><span class="pre">GetoptError</span></tt></a> will be raised.</p>
<p>The return value consists of two elements: the first is a list of <tt class="docutils literal"><span class="pre">(option,</span>
<span class="pre">value)</span></tt> pairs; the second is the list of program arguments left after the
option list was stripped (this is a trailing slice of <em>args</em>). Each
option-and-value pair returned has the option as its first element, prefixed
with a hyphen for short options (e.g., <tt class="docutils literal"><span class="pre">'-x'</span></tt>) or two hyphens for long
options (e.g., <tt class="docutils literal"><span class="pre">'--long-option'</span></tt>), and the option argument as its
second element, or an empty string if the option has no argument. The
options occur in the list in the same order in which they were found, thus
allowing multiple occurrences. Long and short options may be mixed.</p>
</dd></dl>
<dl class="function">
<dt id="getopt.gnu_getopt">
<tt class="descclassname">getopt.</tt><tt class="descname">gnu_getopt</tt><big>(</big><em>args</em>, <em>shortopts</em>, <em>longopts=</em><span class="optional">[</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#getopt.gnu_getopt" title="Permalink to this definition">¶</a></dt>
<dd><p>This function works like <a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-func docutils literal"><span class="pre">getopt()</span></tt></a>, except that GNU style scanning mode is
used by default. This means that option and non-option arguments may be
intermixed. The <a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-func docutils literal"><span class="pre">getopt()</span></tt></a> function stops processing options as soon as a
non-option argument is encountered.</p>
<p>If the first character of the option string is <tt class="docutils literal"><span class="pre">'+'</span></tt>, or if the environment
variable <span class="target" id="index-0"></span><tt class="xref std std-envvar docutils literal"><span class="pre">POSIXLY_CORRECT</span></tt> is set, then option processing stops as
soon as a non-option argument is encountered.</p>
</dd></dl>
<dl class="exception">
<dt id="getopt.GetoptError">
<em class="property">exception </em><tt class="descclassname">getopt.</tt><tt class="descname">GetoptError</tt><a class="headerlink" href="#getopt.GetoptError" title="Permalink to this definition">¶</a></dt>
<dd><p>This is raised when an unrecognized option is found in the argument list or when
an option requiring an argument is given none. The argument to the exception is
a string indicating the cause of the error. For long options, an argument given
to an option which does not require one will also cause this exception to be
raised. The attributes <tt class="xref py py-attr docutils literal"><span class="pre">msg</span></tt> and <tt class="xref py py-attr docutils literal"><span class="pre">opt</span></tt> give the error message and
related option; if there is no specific option to which the exception relates,
<tt class="xref py py-attr docutils literal"><span class="pre">opt</span></tt> is an empty string.</p>
</dd></dl>
<dl class="exception">
<dt id="getopt.error">
<em class="property">exception </em><tt class="descclassname">getopt.</tt><tt class="descname">error</tt><a class="headerlink" href="#getopt.error" title="Permalink to this definition">¶</a></dt>
<dd><p>Alias for <a class="reference internal" href="#getopt.GetoptError" title="getopt.GetoptError"><tt class="xref py py-exc docutils literal"><span class="pre">GetoptError</span></tt></a>; for backward compatibility.</p>
</dd></dl>
<p>An example using only Unix style options:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">getopt</span>
<span class="gp">>>> </span><span class="n">args</span> <span class="o">=</span> <span class="s">'-a -b -cfoo -d bar a1 a2'</span><span class="o">.</span><span class="n">split</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">args</span>
<span class="go">['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']</span>
<span class="gp">>>> </span><span class="n">optlist</span><span class="p">,</span> <span class="n">args</span> <span class="o">=</span> <span class="n">getopt</span><span class="o">.</span><span class="n">getopt</span><span class="p">(</span><span class="n">args</span><span class="p">,</span> <span class="s">'abc:d:'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">optlist</span>
<span class="go">[('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]</span>
<span class="gp">>>> </span><span class="n">args</span>
<span class="go">['a1', 'a2']</span>
</pre></div>
</div>
<p>Using long option names is equally easy:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s">'--condition=foo --testing --output-file abc.def -x a1 a2'</span>
<span class="gp">>>> </span><span class="n">args</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">split</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">args</span>
<span class="go">['--condition=foo', '--testing', '--output-file', 'abc.def', '-x', 'a1', 'a2']</span>
<span class="gp">>>> </span><span class="n">optlist</span><span class="p">,</span> <span class="n">args</span> <span class="o">=</span> <span class="n">getopt</span><span class="o">.</span><span class="n">getopt</span><span class="p">(</span><span class="n">args</span><span class="p">,</span> <span class="s">'x'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s">'condition='</span><span class="p">,</span> <span class="s">'output-file='</span><span class="p">,</span> <span class="s">'testing'</span><span class="p">])</span>
<span class="gp">>>> </span><span class="n">optlist</span>
<span class="go">[('--condition', 'foo'), ('--testing', ''), ('--output-file', 'abc.def'), ('-x', '')]</span>
<span class="gp">>>> </span><span class="n">args</span>
<span class="go">['a1', 'a2']</span>
</pre></div>
</div>
<p>In a script, typical usage is something like this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">getopt</span><span class="o">,</span> <span class="nn">sys</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">opts</span><span class="p">,</span> <span class="n">args</span> <span class="o">=</span> <span class="n">getopt</span><span class="o">.</span><span class="n">getopt</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:],</span> <span class="s">"ho:v"</span><span class="p">,</span> <span class="p">[</span><span class="s">"help"</span><span class="p">,</span> <span class="s">"output="</span><span class="p">])</span>
<span class="k">except</span> <span class="n">getopt</span><span class="o">.</span><span class="n">GetoptError</span> <span class="k">as</span> <span class="n">err</span><span class="p">:</span>
<span class="c"># print help information and exit:</span>
<span class="nb">print</span><span class="p">(</span><span class="n">err</span><span class="p">)</span> <span class="c"># will print something like "option -a not recognized"</span>
<span class="n">usage</span><span class="p">()</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="n">output</span> <span class="o">=</span> <span class="k">None</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="k">False</span>
<span class="k">for</span> <span class="n">o</span><span class="p">,</span> <span class="n">a</span> <span class="ow">in</span> <span class="n">opts</span><span class="p">:</span>
<span class="k">if</span> <span class="n">o</span> <span class="o">==</span> <span class="s">"-v"</span><span class="p">:</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="k">True</span>
<span class="k">elif</span> <span class="n">o</span> <span class="ow">in</span> <span class="p">(</span><span class="s">"-h"</span><span class="p">,</span> <span class="s">"--help"</span><span class="p">):</span>
<span class="n">usage</span><span class="p">()</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">()</span>
<span class="k">elif</span> <span class="n">o</span> <span class="ow">in</span> <span class="p">(</span><span class="s">"-o"</span><span class="p">,</span> <span class="s">"--output"</span><span class="p">):</span>
<span class="n">output</span> <span class="o">=</span> <span class="n">a</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">assert</span> <span class="k">False</span><span class="p">,</span> <span class="s">"unhandled option"</span>
<span class="c"># ...</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>Note that an equivalent command line interface could be produced with less code
and more informative help and error messages by using the <a class="reference internal" href="argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><tt class="xref py py-mod docutils literal"><span class="pre">argparse</span></tt></a> module:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">argparse</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">parser</span> <span class="o">=</span> <span class="n">argparse</span><span class="o">.</span><span class="n">ArgumentParser</span><span class="p">()</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s">'-o'</span><span class="p">,</span> <span class="s">'--output'</span><span class="p">)</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s">'-v'</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s">'verbose'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s">'store_true'</span><span class="p">)</span>
<span class="n">args</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
<span class="c"># ... do something with args.output ...</span>
<span class="c"># ... do something with args.verbose ..</span>
</pre></div>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Module <a class="reference internal" href="argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><tt class="xref py py-mod docutils literal"><span class="pre">argparse</span></tt></a></dt>
<dd>Alternative command line option and argument parsing library.</dd>
</dl>
</div>
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