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<li><a class="reference internal" href="#">dircache – Cache directory listings</a><ul>
<li><a class="reference internal" href="#listing-directory-contents">Listing Directory Contents</a></li>
<li><a class="reference internal" href="#annotated-listings">Annotated Listings</a></li>
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<div class="section" id="module-dircache">
<span id="dircache-cache-directory-listings"></span><h1>dircache – Cache directory listings<a class="headerlink" href="#module-dircache" 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">Cache directory listings, updating when the modification time of a directory changes.</td>
</tr>
<tr class="field"><th class="field-name">Python Version:</th><td class="field-body">1.4 and later</td>
</tr>
</tbody>
</table>
<div class="section" id="listing-directory-contents">
<h2>Listing Directory Contents<a class="headerlink" href="#listing-directory-contents" title="Permalink to this headline">¶</a></h2>
<p>The main function in the <a class="reference internal" href="#module-dircache" title="dircache: Cache directory listings"><tt class="xref py py-mod docutils literal"><span class="pre">dircache</span></tt></a> API is <tt class="xref py py-func docutils literal"><span class="pre">listdir()</span></tt>, a
wrapper around <tt class="xref py py-func docutils literal"><span class="pre">os.listdir()</span></tt> that caches the results and returns
the same <tt class="xref py py-class docutils literal"><span class="pre">list</span></tt> each time it is called with a given path, unless the
modification date of the named directory changes.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">dircache</span>
<span class="n">path</span> <span class="o">=</span> <span class="s">'.'</span>
<span class="n">first</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="n">second</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'Contents :'</span><span class="p">,</span> <span class="n">first</span>
<span class="k">print</span> <span class="s">'Identical:'</span><span class="p">,</span> <span class="n">first</span> <span class="ow">is</span> <span class="n">second</span>
<span class="k">print</span> <span class="s">'Equal :'</span><span class="p">,</span> <span class="n">first</span> <span class="o">==</span> <span class="n">second</span>
</pre></div>
</div>
<p>It is important to recognize that the exact same <tt class="xref py py-class docutils literal"><span class="pre">list</span></tt> is
returned each time, so it should not be modified in place.</p>
<div class="highlight-python"><pre>$ python dircache_listdir.py
Contents : ['__init__.py', 'dircache_annotate.py', 'dircache_listdir.py', 'dircache_listdir_file_added.py', 'dircache_reset.py', 'index.rst']
Identical: True
Equal : True</pre>
</div>
<p>If the contents of the directory changes, it is rescanned.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">dircache</span>
<span class="kn">import</span> <span class="nn">os</span>
<span class="n">path</span> <span class="o">=</span> <span class="s">'/tmp'</span>
<span class="n">file_to_create</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">path</span><span class="p">,</span> <span class="s">'pymotw_tmp.txt'</span><span class="p">)</span>
<span class="c"># Look at the directory contents</span>
<span class="n">first</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="c"># Create the new file</span>
<span class="nb">open</span><span class="p">(</span><span class="n">file_to_create</span><span class="p">,</span> <span class="s">'wt'</span><span class="p">)</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="c"># Rescan the directory</span>
<span class="n">second</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="c"># Remove the file we created</span>
<span class="n">os</span><span class="o">.</span><span class="n">unlink</span><span class="p">(</span><span class="n">file_to_create</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'Identical :'</span><span class="p">,</span> <span class="n">first</span> <span class="ow">is</span> <span class="n">second</span>
<span class="k">print</span> <span class="s">'Equal :'</span><span class="p">,</span> <span class="n">first</span> <span class="o">==</span> <span class="n">second</span>
<span class="k">print</span> <span class="s">'Difference:'</span><span class="p">,</span> <span class="nb">list</span><span class="p">(</span><span class="nb">set</span><span class="p">(</span><span class="n">second</span><span class="p">)</span> <span class="o">-</span> <span class="nb">set</span><span class="p">(</span><span class="n">first</span><span class="p">))</span>
</pre></div>
</div>
<p>In this case the new file causes a new <tt class="xref py py-class docutils literal"><span class="pre">list</span></tt> to be
constructed.</p>
<div class="highlight-python"><pre>$ python dircache_listdir_file_added.py
Identical : False
Equal : False
Difference: ['pymotw_tmp.txt']</pre>
</div>
<p>It is also possible to reset the entire cache, discarding its contents so that
each path will be rechecked.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">dircache</span>
<span class="n">path</span> <span class="o">=</span> <span class="s">'/tmp'</span>
<span class="n">first</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="n">dircache</span><span class="o">.</span><span class="n">reset</span><span class="p">()</span>
<span class="n">second</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="k">print</span> <span class="s">'Identical :'</span><span class="p">,</span> <span class="n">first</span> <span class="ow">is</span> <span class="n">second</span>
<span class="k">print</span> <span class="s">'Equal :'</span><span class="p">,</span> <span class="n">first</span> <span class="o">==</span> <span class="n">second</span>
<span class="k">print</span> <span class="s">'Difference:'</span><span class="p">,</span> <span class="nb">list</span><span class="p">(</span><span class="nb">set</span><span class="p">(</span><span class="n">second</span><span class="p">)</span> <span class="o">-</span> <span class="nb">set</span><span class="p">(</span><span class="n">first</span><span class="p">))</span>
</pre></div>
</div>
<p>After resetting, a new <tt class="xref py py-class docutils literal"><span class="pre">list</span></tt> instance is returned.</p>
<div class="highlight-python"><pre>$ python dircache_reset.py
Identical : False
Equal : True
Difference: []</pre>
</div>
</div>
<div class="section" id="annotated-listings">
<h2>Annotated Listings<a class="headerlink" href="#annotated-listings" title="Permalink to this headline">¶</a></h2>
<p>The other interesting function provided by the dircache module is
<tt class="xref py py-func docutils literal"><span class="pre">annotate()</span></tt>. When called, <tt class="xref py py-func docutils literal"><span class="pre">annotate()</span></tt> modifies a
<tt class="xref py py-func docutils literal"><span class="pre">list()</span></tt> such as is returned by <tt class="xref py py-func docutils literal"><span class="pre">listdir()</span></tt>, adding a <tt class="docutils literal"><span class="pre">'/'</span></tt>
to the end of the names that represent directories.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">dircache</span>
<span class="kn">from</span> <span class="nn">pprint</span> <span class="kn">import</span> <span class="n">pprint</span>
<span class="kn">import</span> <span class="nn">os</span>
<span class="n">path</span> <span class="o">=</span> <span class="s">'../..'</span>
<span class="n">contents</span> <span class="o">=</span> <span class="n">dircache</span><span class="o">.</span><span class="n">listdir</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="n">annotated</span> <span class="o">=</span> <span class="n">contents</span><span class="p">[:]</span>
<span class="n">dircache</span><span class="o">.</span><span class="n">annotate</span><span class="p">(</span><span class="n">path</span><span class="p">,</span> <span class="n">annotated</span><span class="p">)</span>
<span class="n">fmt</span> <span class="o">=</span> <span class="s">'</span><span class="si">%25s</span><span class="se">\t</span><span class="si">%25s</span><span class="s">'</span>
<span class="k">print</span> <span class="n">fmt</span> <span class="o">%</span> <span class="p">(</span><span class="s">'ORIGINAL'</span><span class="p">,</span> <span class="s">'ANNOTATED'</span><span class="p">)</span>
<span class="k">print</span> <span class="n">fmt</span> <span class="o">%</span> <span class="p">((</span><span class="s">'-'</span> <span class="o">*</span> <span class="mi">25</span><span class="p">,)</span><span class="o">*</span><span class="mi">2</span><span class="p">)</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="nb">zip</span><span class="p">(</span><span class="n">contents</span><span class="p">,</span> <span class="n">annotated</span><span class="p">):</span>
<span class="k">print</span> <span class="n">fmt</span> <span class="o">%</span> <span class="p">(</span><span class="n">o</span><span class="p">,</span> <span class="n">a</span><span class="p">)</span>
</pre></div>
</div>
<p>Unfortunately for Windows users, although <tt class="xref py py-func docutils literal"><span class="pre">annotate()</span></tt> uses
<tt class="xref py py-func docutils literal"><span class="pre">os.path.join()</span></tt> to construct names to test, it always appends a
<tt class="docutils literal"><span class="pre">'/'</span></tt>, not <tt class="xref py py-data docutils literal"><span class="pre">os.sep</span></tt>.</p>
<div class="highlight-python"><pre>$ python dircache_annotate.py
ORIGINAL ANNOTATED
------------------------- -------------------------
.hg .hg/
.hgignore .hgignore
.hgtags .hgtags
LICENSE.txt LICENSE.txt
MANIFEST.in MANIFEST.in
PyMOTW PyMOTW/
PyMOTW.egg-info PyMOTW.egg-info/
README.txt README.txt
bin bin/
blog_posts blog_posts/
dist dist/
module module
motw motw
pavement.py pavement.py
paver-minilib.zip paver-minilib.zip
setup.py setup.py
sitemap_gen_config.xml sitemap_gen_config.xml
sphinx sphinx/
utils utils/
web web/</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/dircache.html">dircache</a></dt>
<dd>The standard library documentation for this module.</dd>
</dl>
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