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<h1>Documentation<a class="headerlink" href="#documentation" title="Permalink to this headline">¶</a></h1>
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<li class="toctree-l1"><a class="reference external" href="overview.html">Introduction to argparse</a><ul>
<li class="toctree-l2"><a class="reference external" href="overview.html#adding-arguments">Adding arguments</a></li>
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<li class="toctree-l2"><a class="reference external" href="ArgumentParser.html">ArgumentParser objects</a></li>
<li class="toctree-l2"><a class="reference external" href="add_argument.html">The add_argument() method</a></li>
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<h1>Example usage<a class="headerlink" href="#example-usage" title="Permalink to this headline">¶</a></h1>
<p>The following simple example uses the argparse module to generate the command-line interface for a Python program that sums its command-line arguments and writes them to a log file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">argparse</span>
<span class="kn">import</span> <span class="nn">sys</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="c"># create the parser</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">description</span><span class="o">=</span><span class="s">'Sum the integers on the command line.'</span><span class="p">)</span>
<span class="c"># add the arguments</span>
<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
<span class="s">'integers'</span><span class="p">,</span> <span class="n">metavar</span><span class="o">=</span><span class="s">'int'</span><span class="p">,</span> <span class="nb">type</span><span class="o">=</span><span class="nb">int</span><span class="p">,</span> <span class="n">nargs</span><span class="o">=</span><span class="s">'+'</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'one of the integers to be summed'</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">'--log'</span><span class="p">,</span> <span class="nb">type</span><span class="o">=</span><span class="n">argparse</span><span class="o">.</span><span class="n">FileType</span><span class="p">(</span><span class="s">'w'</span><span class="p">),</span> <span class="n">default</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">,</span>
<span class="n">help</span><span class="o">=</span><span class="s">'the file where the sum should be written '</span>
<span class="s">'(default: write the sum to stdout)'</span><span class="p">)</span>
<span class="c"># parse the command line</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"># write out the sum</span>
<span class="n">args</span><span class="o">.</span><span class="n">log</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'</span><span class="si">%s</span><span class="se">\n</span><span class="s">'</span> <span class="o">%</span> <span class="nb">sum</span><span class="p">(</span><span class="n">args</span><span class="o">.</span><span class="n">integers</span><span class="p">))</span>
<span class="n">args</span><span class="o">.</span><span class="n">log</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
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<p>Assuming the Python code above is saved into a file called <tt class="docutils literal"><span class="pre">scriptname.py</span></tt>, it can be run at the command line and provides useful help messages:</p>
<div class="highlight-python"><pre>$ scriptname.py -h
usage: scriptname.py [-h] [--log LOG] int [int ...]
Sum the integers on the command line.
positional arguments:
int one of the integers to be summed
optional arguments:
-h, --help show this help message and exit
--log LOG the file where the sum should be written (default: write the sum
to stdout)</pre>
</div>
<p>When run with the appropriate arguments, it writes the sum of the command-line integers to the specified log file:</p>
<div class="highlight-python"><pre>$ scriptname.py --log=log.txt 1 1 2 3 5 8
$ more log.txt
20</pre>
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