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<div class="section" id="module-getopt">
<span id="getopt-c-style-parser-for-command-line-options"></span><h1><a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><code class="xref py py-mod docutils literal notranslate"><span class="pre">getopt</span></code></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="https://github.com/python/cpython/tree/3.7/Lib/getopt.py">Lib/getopt.py</a></p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <a class="reference internal" href="#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><code class="xref py py-mod docutils literal notranslate"><span class="pre">getopt</span></code></a> module is a parser for command line options whose API is
designed to be familiar to users of the C <code class="xref c c-func docutils literal notranslate"><span class="pre">getopt()</span></code> function. Users who
are unfamiliar with the C <code class="xref c c-func docutils literal notranslate"><span class="pre">getopt()</span></code> 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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">argparse</span></code></a> module instead.</p>
</div>
<hr class="docutils" />
<p>This module helps scripts to parse the command line arguments in <code class="docutils literal notranslate"><span class="pre">sys.argv</span></code>.
It supports the same conventions as the Unix <code class="xref c c-func docutils literal notranslate"><span class="pre">getopt()</span></code> function (including
the special meanings of arguments of the form ‘<code class="docutils literal notranslate"><span class="pre">-</span></code>‘ and ‘<code class="docutils literal notranslate"><span class="pre">--</span></code>‘). 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">
<code class="sig-prename descclassname">getopt.</code><code class="sig-name descname">getopt</code><span class="sig-paren">(</span><em class="sig-param">args</em>, <em class="sig-param">shortopts</em>, <em class="sig-param">longopts=[]</em><span class="sig-paren">)</span><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 <code class="docutils literal notranslate"><span class="pre">sys.argv[1:]</span></code>. <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 (<code class="docutils literal notranslate"><span class="pre">':'</span></code>; i.e., the same format that Unix <code class="xref c c-func docutils literal notranslate"><span class="pre">getopt()</span></code> uses).</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Unlike GNU <code class="xref c c-func docutils literal notranslate"><span class="pre">getopt()</span></code>, 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 <code class="docutils literal notranslate"><span class="pre">'--'</span></code> characters
should not be included in the option name. Long options which require an
argument should be followed by an equal sign (<code class="docutils literal notranslate"><span class="pre">'='</span></code>). 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 <code class="docutils literal notranslate"><span class="pre">['foo',</span> <span class="pre">'frob']</span></code>, the
option <code class="docutils literal notranslate"><span class="pre">--fo</span></code> will match as <code class="docutils literal notranslate"><span class="pre">--foo</span></code>, but <code class="docutils literal notranslate"><span class="pre">--f</span></code> will
not match uniquely, so <a class="reference internal" href="#getopt.GetoptError" title="getopt.GetoptError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GetoptError</span></code></a> will be raised.</p>
<p>The return value consists of two elements: the first is a list of <code class="docutils literal notranslate"><span class="pre">(option,</span>
<span class="pre">value)</span></code> 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., <code class="docutils literal notranslate"><span class="pre">'-x'</span></code>) or two hyphens for long
options (e.g., <code class="docutils literal notranslate"><span class="pre">'--long-option'</span></code>), 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">
<code class="sig-prename descclassname">getopt.</code><code class="sig-name descname">gnu_getopt</code><span class="sig-paren">(</span><em class="sig-param">args</em>, <em class="sig-param">shortopts</em>, <em class="sig-param">longopts=[]</em><span class="sig-paren">)</span><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."><code class="xref py py-func docutils literal notranslate"><span class="pre">getopt()</span></code></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."><code class="xref py py-func docutils literal notranslate"><span class="pre">getopt()</span></code></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 <code class="docutils literal notranslate"><span class="pre">'+'</span></code>, or if the environment
variable <span class="target" id="index-0"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">POSIXLY_CORRECT</span></code> 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><code class="sig-prename descclassname">getopt.</code><code class="sig-name descname">GetoptError</code><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 <code class="xref py py-attr docutils literal notranslate"><span class="pre">msg</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">opt</span></code> give the error message and
related option; if there is no specific option to which the exception relates,
<code class="xref py py-attr docutils literal notranslate"><span class="pre">opt</span></code> is an empty string.</p>
</dd></dl>
<dl class="exception">
<dt id="getopt.error">
<em class="property">exception </em><code class="sig-prename descclassname">getopt.</code><code class="sig-name descname">error</code><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"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GetoptError</span></code></a>; for backward compatibility.</p>
</dd></dl>
<p>An example using only Unix style options:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><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="s1">'-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="s1">'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="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s1">'--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="s1">'x'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s1">'condition='</span><span class="p">,</span> <span class="s1">'output-file='</span><span class="p">,</span> <span class="s1">'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 notranslate"><div class="highlight"><pre><span></span><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="s2">"ho:v"</span><span class="p">,</span> <span class="p">[</span><span class="s2">"help"</span><span class="p">,</span> <span class="s2">"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="c1"># 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="c1"># 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="kc">None</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">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="s2">"-v"</span><span class="p">:</span>
<span class="n">verbose</span> <span class="o">=</span> <span class="kc">True</span>
<span class="k">elif</span> <span class="n">o</span> <span class="ow">in</span> <span class="p">(</span><span class="s2">"-h"</span><span class="p">,</span> <span class="s2">"--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="s2">"-o"</span><span class="p">,</span> <span class="s2">"--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="kc">False</span><span class="p">,</span> <span class="s2">"unhandled option"</span>
<span class="c1"># ...</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s2">"__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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">argparse</span></code></a> module:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">argparse</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__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="s1">'-o'</span><span class="p">,</span> <span class="s1">'--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="s1">'-v'</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">'verbose'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s1">'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="c1"># ... do something with args.output ...</span>
<span class="c1"># ... do something with args.verbose ..</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt>Module <a class="reference internal" href="argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate"><span class="pre">argparse</span></code></a></dt><dd><p>Alternative command line option and argument parsing library.</p>
</dd>
</dl>
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