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<li><a class="reference internal" href="#">fileinput &#8211; Process lines from input streams</a><ul>
<li><a class="reference internal" href="#converting-m3u-files-to-rss">Converting M3U files to RSS</a></li>
<li><a class="reference internal" href="#progress-meta-data">Progress Meta-data</a></li>
<li><a class="reference internal" href="#in-place-filtering">In-place Filtering</a></li>
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  <div class="section" id="module-fileinput">
<span id="fileinput-process-lines-from-input-streams"></span><h1>fileinput &#8211; Process lines from input streams<a class="headerlink" href="#module-fileinput" title="Permalink to this headline">¶</a></h1>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Purpose:</th><td class="field-body">Create command-line filter programs to process lines from input streams.</td>
</tr>
<tr class="field"><th class="field-name">Python Version:</th><td class="field-body">1.5.2 and later</td>
</tr>
</tbody>
</table>
<p>The fileinput module is a framework for creating command line programs
for processing text files in a filter-ish manner.</p>
<div class="section" id="converting-m3u-files-to-rss">
<h2>Converting M3U files to RSS<a class="headerlink" href="#converting-m3u-files-to-rss" title="Permalink to this headline">¶</a></h2>
<p>For example, the
<a class="reference external" href="http://www.doughellmann.com/projects/m3utorss">m3utorss</a> app I recently wrote for my friend <a class="reference external" href="http://events.mediumloud.com/">Patrick</a> to convert some of his demo
recordings into a podcastable format.</p>
<p>The inputs to the program are one or more m3u file listing the mp3 files to be
distributed. The output is a single blob of XML that looks like an RSS feed
(output is written to stdout, for simplicity). To process the input, I need to
iterate over the list of filenames and:</p>
<ul class="simple">
<li>Open each file.</li>
<li>Read each line of the file.</li>
<li>Figure out if the line refers to an mp3 file.</li>
<li>If it does, extract the information from the mp3 file needed for the RSS feed.</li>
<li>Print the output.</li>
</ul>
<p>I could have written all of that file handling out by hand. It isn&#8217;t that
complicated, and with some testing I&#8217;m sure I could even get the error
handling right. But with the fileinput module, I don&#8217;t need to worry about
that. I just write something like:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">input</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="n">mp3filename</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
    <span class="k">if</span> <span class="ow">not</span> <span class="n">mp3filename</span> <span class="ow">or</span> <span class="n">mp3filename</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s">&#39;#&#39;</span><span class="p">):</span>
        <span class="k">continue</span>
    <span class="n">item</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">rss</span><span class="p">,</span> <span class="s">&#39;item&#39;</span><span class="p">)</span>
    <span class="n">title</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">item</span><span class="p">,</span> <span class="s">&#39;title&#39;</span><span class="p">)</span>
    <span class="n">title</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="n">mp3filename</span>
    <span class="n">encl</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">item</span><span class="p">,</span> <span class="s">&#39;enclosure&#39;</span><span class="p">,</span> <span class="p">{</span><span class="s">&#39;type&#39;</span><span class="p">:</span><span class="s">&#39;audio/mpeg&#39;</span><span class="p">,</span> <span class="s">&#39;url&#39;</span><span class="p">:</span><span class="n">mp3filename</span><span class="p">})</span>
</pre></div>
</div>
<p>The <tt class="docutils literal"><span class="pre">fileinput.input()</span></tt> function takes as argument a list of
filenames to examine. If the list is empty, the module reads data from
standard input. The function returns an iterator which returns
individual lines from the text files being processed.  So, all I have
to do is loop over each line, skipping blanks and comments, to find
the references to mp3 files.</p>
<p>Here&#8217;s the complete program:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">fileinput</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="kn">import</span> <span class="nn">time</span>
<span class="kn">from</span> <span class="nn">xml.etree.ElementTree</span> <span class="kn">import</span> <span class="n">Element</span><span class="p">,</span> <span class="n">SubElement</span><span class="p">,</span> <span class="n">tostring</span>
<span class="kn">from</span> <span class="nn">xml.dom</span> <span class="kn">import</span> <span class="n">minidom</span>

<span class="c"># Establish the RSS and channel nodes</span>
<span class="n">rss</span> <span class="o">=</span> <span class="n">Element</span><span class="p">(</span><span class="s">&#39;rss&#39;</span><span class="p">,</span> <span class="p">{</span><span class="s">&#39;xmlns:dc&#39;</span><span class="p">:</span><span class="s">&quot;http://purl.org/dc/elements/1.1/&quot;</span><span class="p">,</span>
                      <span class="s">&#39;version&#39;</span><span class="p">:</span><span class="s">&#39;2.0&#39;</span><span class="p">,</span>
                      <span class="p">})</span>
<span class="n">channel</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">rss</span><span class="p">,</span> <span class="s">&#39;channel&#39;</span><span class="p">)</span>
<span class="n">title</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">channel</span><span class="p">,</span> <span class="s">&#39;title&#39;</span><span class="p">)</span>
<span class="n">title</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">&#39;Sample podcast feed&#39;</span>
<span class="n">desc</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">channel</span><span class="p">,</span> <span class="s">&#39;description&#39;</span><span class="p">)</span>
<span class="n">desc</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">&#39;Generated for PyMOTW&#39;</span>
<span class="n">pubdate</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">channel</span><span class="p">,</span> <span class="s">&#39;pubDate&#39;</span><span class="p">)</span>
<span class="n">pubdate</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="n">time</span><span class="o">.</span><span class="n">asctime</span><span class="p">()</span>
<span class="n">gen</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">channel</span><span class="p">,</span> <span class="s">&#39;generator&#39;</span><span class="p">)</span>
<span class="n">gen</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">&#39;http://www.doughellmann.com/PyMOTW/&#39;</span>

<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">input</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="n">mp3filename</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
    <span class="k">if</span> <span class="ow">not</span> <span class="n">mp3filename</span> <span class="ow">or</span> <span class="n">mp3filename</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s">&#39;#&#39;</span><span class="p">):</span>
        <span class="k">continue</span>
    <span class="n">item</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">rss</span><span class="p">,</span> <span class="s">&#39;item&#39;</span><span class="p">)</span>
    <span class="n">title</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">item</span><span class="p">,</span> <span class="s">&#39;title&#39;</span><span class="p">)</span>
    <span class="n">title</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="n">mp3filename</span>
    <span class="n">encl</span> <span class="o">=</span> <span class="n">SubElement</span><span class="p">(</span><span class="n">item</span><span class="p">,</span> <span class="s">&#39;enclosure&#39;</span><span class="p">,</span> <span class="p">{</span><span class="s">&#39;type&#39;</span><span class="p">:</span><span class="s">&#39;audio/mpeg&#39;</span><span class="p">,</span> <span class="s">&#39;url&#39;</span><span class="p">:</span><span class="n">mp3filename</span><span class="p">})</span>
        
<span class="n">rough_string</span> <span class="o">=</span> <span class="n">tostring</span><span class="p">(</span><span class="n">rss</span><span class="p">)</span>
<span class="n">reparsed</span> <span class="o">=</span> <span class="n">minidom</span><span class="o">.</span><span class="n">parseString</span><span class="p">(</span><span class="n">rough_string</span><span class="p">)</span>
<span class="k">print</span> <span class="n">reparsed</span><span class="o">.</span><span class="n">toprettyxml</span><span class="p">(</span><span class="n">indent</span><span class="o">=</span><span class="s">&quot;  &quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>and its output:</p>
<div class="highlight-python"><pre>$ python fileinput_example.py sample_data.m3u

&lt;?xml version="1.0" ?&gt;
&lt;rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/"&gt;
  &lt;channel&gt;
    &lt;title&gt;
      Sample podcast feed
    &lt;/title&gt;
    &lt;description&gt;
      Generated for PyMOTW
    &lt;/description&gt;
    &lt;pubDate&gt;
      Sun Oct 24 08:53:34 2010
    &lt;/pubDate&gt;
    &lt;generator&gt;
      http://www.doughellmann.com/PyMOTW/
    &lt;/generator&gt;
  &lt;/channel&gt;
  &lt;item&gt;
    &lt;title&gt;
      episode-one.mp3
    &lt;/title&gt;
    &lt;enclosure type="audio/mpeg" url="episode-one.mp3"/&gt;
  &lt;/item&gt;
  &lt;item&gt;
    &lt;title&gt;
      episode-two.mp3
    &lt;/title&gt;
    &lt;enclosure type="audio/mpeg" url="episode-two.mp3"/&gt;
  &lt;/item&gt;
&lt;/rss&gt;</pre>
</div>
</div>
<div class="section" id="progress-meta-data">
<h2>Progress Meta-data<a class="headerlink" href="#progress-meta-data" title="Permalink to this headline">¶</a></h2>
<p>In the previous example, I did not care what file or line number we
are processing in the input. For other tools (grep-like searching, for
example) you might. The fileinput module includes functions for
accessing that information (<tt class="docutils literal"><span class="pre">filename()</span></tt>, <tt class="docutils literal"><span class="pre">filelineno()</span></tt>,
<tt class="docutils literal"><span class="pre">lineno()</span></tt>, etc.).</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">fileinput</span>
<span class="kn">import</span> <span class="nn">re</span>
<span class="kn">import</span> <span class="nn">sys</span>

<span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</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="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">input</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">2</span><span class="p">:]):</span>
    <span class="k">if</span> <span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">line</span><span class="p">):</span>
        <span class="k">if</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">isstdin</span><span class="p">():</span>
            <span class="n">fmt</span> <span class="o">=</span> <span class="s">&#39;{lineno}:{line}&#39;</span>
        <span class="k">else</span><span class="p">:</span>
            <span class="n">fmt</span> <span class="o">=</span> <span class="s">&#39;{filename:&lt;20}:{lineno}:{line}&#39;</span>
        <span class="k">print</span> <span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">filename</span><span class="o">=</span><span class="n">fileinput</span><span class="o">.</span><span class="n">filename</span><span class="p">(),</span>
                         <span class="n">lineno</span><span class="o">=</span><span class="n">fileinput</span><span class="o">.</span><span class="n">filelineno</span><span class="p">(),</span>
                         <span class="n">line</span><span class="o">=</span><span class="n">line</span><span class="o">.</span><span class="n">rstrip</span><span class="p">())</span>
</pre></div>
</div>
<p>We can use this basic pattern matching loop to find the occurances of
&#8220;fileinput&#8221; in the source for the examples.</p>
<div class="highlight-python"><pre>$ python fileinput_grep.py fileinput *.py

fileinput_change_subnet.py:10:import fileinput
fileinput_change_subnet.py:17:for line in fileinput.input(files, inplace=True):
fileinput_change_subnet_noisy.py:10:import fileinput
fileinput_change_subnet_noisy.py:18:for line in fileinput.input(files, inplace=True):
fileinput_change_subnet_noisy.py:19:    if fileinput.isfirstline():
fileinput_change_subnet_noisy.py:20:        sys.stderr.write('Started processing %s\n' % fileinput.filename())
fileinput_example.py:6:"""Example for fileinput module.
fileinput_example.py:10:import fileinput
fileinput_example.py:30:for line in fileinput.input(sys.argv[1:]):
fileinput_grep.py   :10:import fileinput
fileinput_grep.py   :16:for line in fileinput.input(sys.argv[2:]):
fileinput_grep.py   :18:        if fileinput.isstdin():
fileinput_grep.py   :22:        print fmt.format(filename=fileinput.filename(),
fileinput_grep.py   :23:                         lineno=fileinput.filelineno(),</pre>
</div>
<p>We can also pass input to it through stdin.</p>
<div class="highlight-python"><pre>$ cat *.py | python fileinput_grep.py fileinput

10:import fileinput
17:for line in fileinput.input(files, inplace=True):
29:import fileinput
37:for line in fileinput.input(files, inplace=True):
38:    if fileinput.isfirstline():
39:        sys.stderr.write('Started processing %s\n' % fileinput.filename())
51:"""Example for fileinput module.
55:import fileinput
75:for line in fileinput.input(sys.argv[1:]):
96:import fileinput
102:for line in fileinput.input(sys.argv[2:]):
104:        if fileinput.isstdin():
108:        print fmt.format(filename=fileinput.filename(),
109:                         lineno=fileinput.filelineno(),</pre>
</div>
</div>
<div class="section" id="in-place-filtering">
<h2>In-place Filtering<a class="headerlink" href="#in-place-filtering" title="Permalink to this headline">¶</a></h2>
<p>Another common file processing operation is to modify the contents.
For example, a Unix hosts file might need to be updated if a subnet
range changes.</p>
<div class="highlight-python"><pre>##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1       localhost
255.255.255.255 broadcasthost
::1             localhost 
fe80::1%lo0     localhost
172.16.177.128  hubert hubert.hellfly.net
172.16.177.132  cubert cubert.hellfly.net
172.16.177.136  zoidberg zoidberg.hellfly.net
</pre>
</div>
<p>The safe way to make the change automatically is to create a new file
based on the input and then replace the original with the edited copy.
fileinput supports this automatically using the <em>inplace</em> option.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">fileinput</span>
<span class="kn">import</span> <span class="nn">sys</span>

<span class="n">from_base</span> <span class="o">=</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="n">to_base</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>
<span class="n">files</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">3</span><span class="p">:]</span>

<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">input</span><span class="p">(</span><span class="n">files</span><span class="p">,</span> <span class="n">inplace</span><span class="o">=</span><span class="bp">True</span><span class="p">):</span>
    <span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="n">from_base</span><span class="p">,</span> <span class="n">to_base</span><span class="p">)</span>
    <span class="k">print</span> <span class="n">line</span>
</pre></div>
</div>
<div class="highlight-python"><pre>$ python fileinput_change_subnet.py 172.16.177 172.16.178 etc_hosts.txt</pre>
</div>
<p>Although the script uses <tt class="docutils literal"><span class="pre">print</span></tt>, no output is produced to stdout
because fileinput maps stdout to the file being overwritten.</p>
<div class="highlight-python"><pre>##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1       localhost
255.255.255.255 broadcasthost
::1             localhost
fe80::1%lo0     localhost
172.16.178.128  hubert hubert.hellfly.net
172.16.178.132  cubert cubert.hellfly.net
172.16.178.136  zoidberg zoidberg.hellfly.net
</pre>
</div>
<p>Before processing begins, a backup file is created using the original
name plus <tt class="docutils literal"><span class="pre">.bak</span></tt>.  The backup file is removed when the input is
closed.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">fileinput</span>
<span class="kn">import</span> <span class="nn">glob</span>
<span class="kn">import</span> <span class="nn">sys</span>

<span class="n">from_base</span> <span class="o">=</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="n">to_base</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>
<span class="n">files</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">3</span><span class="p">:]</span>

<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">input</span><span class="p">(</span><span class="n">files</span><span class="p">,</span> <span class="n">inplace</span><span class="o">=</span><span class="bp">True</span><span class="p">):</span>
    <span class="k">if</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">isfirstline</span><span class="p">():</span>
        <span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">&#39;Started processing </span><span class="si">%s</span><span class="se">\n</span><span class="s">&#39;</span> <span class="o">%</span> <span class="n">fileinput</span><span class="o">.</span><span class="n">filename</span><span class="p">())</span>
        <span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">&#39;Directory contains: </span><span class="si">%s</span><span class="se">\n</span><span class="s">&#39;</span> <span class="o">%</span> <span class="n">glob</span><span class="o">.</span><span class="n">glob</span><span class="p">(</span><span class="s">&#39;etc_hosts.txt*&#39;</span><span class="p">))</span>
    <span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="n">from_base</span><span class="p">,</span> <span class="n">to_base</span><span class="p">)</span>
    <span class="k">print</span> <span class="n">line</span>

<span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">&#39;Finished processing</span><span class="se">\n</span><span class="s">&#39;</span><span class="p">)</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">&#39;Directory contains: </span><span class="si">%s</span><span class="se">\n</span><span class="s">&#39;</span> <span class="o">%</span> <span class="n">glob</span><span class="o">.</span><span class="n">glob</span><span class="p">(</span><span class="s">&#39;etc_hosts.txt*&#39;</span><span class="p">))</span>
</pre></div>
</div>
<div class="highlight-python"><pre>$ python fileinput_change_subnet_noisy.py 172.16.177 172.16.178 etc_hosts.txt

Started processing etc_hosts.txt
Directory contains: ['etc_hosts.txt', 'etc_hosts.txt.bak']
Finished processing
Directory contains: ['etc_hosts.txt']</pre>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://docs.python.org/library/fileinput.html">fileinput</a></dt>
<dd>The standard library documentation for this module.</dd>
<dt><a class="reference external" href="http://events.mediumloud.com/">Patrick Bryant</a></dt>
<dd>Atlanta-based singer/song-writer.</dd>
<dt><a class="reference external" href="http://www.doughellmann.com/projects/m3utorss">m3utorss</a></dt>
<dd>Script to convert m3u files listing MP3s to an RSS file
suitable for use as a podcast feed.</dd>
<dt><a class="reference internal" href="../xml/etree/ElementTree/create.html#xml-etree-elementtree-creating"><em>Creating XML Documents</em></a></dt>
<dd>More details of using ElementTree to produce XML.</dd>
<dt><a class="reference internal" href="../articles/file_access.html#article-file-access"><em>File Access</em></a></dt>
<dd>Other modules for working with files.</dd>
<dt><a class="reference internal" href="../articles/text_processing.html#article-text-processing"><em>Text Processing Tools</em></a></dt>
<dd>Other modules for working with text.</dd>
</dl>
</div>
</div>
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