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<li><a class="reference internal" href="#">tabnanny – Indentation validator</a><ul>
<li><a class="reference internal" href="#running-from-the-command-line">Running from the Command Line</a></li>
<li><a class="reference internal" href="#using-within-your-program">Using within Your Program</a></li>
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<div class="section" id="module-tabnanny">
<span id="tabnanny-indentation-validator"></span><h1>tabnanny – Indentation validator<a class="headerlink" href="#module-tabnanny" 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">Scan Python source code looking for suspicious indentation.</td>
</tr>
<tr class="field"><th class="field-name">Python Version:</th><td class="field-body">2.1.3 and later</td>
</tr>
</tbody>
</table>
<p>Consistent use of indentation is important in a langauge like Python,
where white-space is significant. The <a class="reference internal" href="#module-tabnanny" title="tabnanny: Scan Python source code looking for suspicious indentation."><tt class="xref py py-mod docutils literal"><span class="pre">tabnanny</span></tt></a> module provides
a scanner to report on “ambiguous” use of indentation.</p>
<div class="section" id="running-from-the-command-line">
<h2>Running from the Command Line<a class="headerlink" href="#running-from-the-command-line" title="Permalink to this headline">¶</a></h2>
<p>The simplest way to use <a class="reference internal" href="#module-tabnanny" title="tabnanny: Scan Python source code looking for suspicious indentation."><tt class="xref py py-mod docutils literal"><span class="pre">tabnanny</span></tt></a> is to run it from the command
line, passing the names of files to check. If you pass directory
names, the directories are scanned recursively to find <cite>.py</cite> files to
check.</p>
<p>When I ran tabnanny across the PyMOTW source code, I found one old
module with tabs instead of spaces:</p>
<div class="highlight-python"><pre>$ python -m tabnanny .
./PyMOTW/Queue/fetch_podcasts.py 78 "\t\tfor enclosure in entry.get('enclosures', []):\n"</pre>
</div>
<p>Sure enough, line 78 of <cite>fetch_podcasts.py</cite> had two tabs instead of 8
spaces. I didn’t see this by looking at it in my editor because I
have my tabstops set to 4 spaces, so visually there was no difference.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">enclosure</span> <span class="ow">in</span> <span class="n">entry</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'enclosures'</span><span class="p">,</span> <span class="p">[]):</span>
<span class="k">print</span> <span class="s">'Queuing:'</span><span class="p">,</span> <span class="n">enclosure</span><span class="p">[</span><span class="s">'url'</span><span class="p">]</span>
<span class="n">enclosure_queue</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="n">enclosure</span><span class="p">[</span><span class="s">'url'</span><span class="p">])</span>
</pre></div>
</div>
<p>Correcting line 78 and running tabnanny again showed another error on
line 79. One last problem showed up on line 80.</p>
<p>If you want to scan files, but not see the details about the error,
you can use the <cite>-q</cite> option to suppress all information except the
filename.</p>
<div class="highlight-python"><pre>$ python -m tabnanny -q .
./PyMOTW/Queue/fetch_podcasts.py</pre>
</div>
<p>To see more information about the files being scanned, use the <cite>-v</cite> option.</p>
<div class="highlight-python"><pre>$ python -m tabnanny -v ./PyMOTW/Queue
'./PyMOTW/Queue': listing directory
'./PyMOTW/Queue/__init__.py': Clean bill of health.
'./PyMOTW/Queue/feedparser.py': Clean bill of health.
'./PyMOTW/Queue/fetch_podcasts.py': *** Line 78: trouble in tab city! ***
offending line: "\t\tfor enclosure in entry.get('enclosures', []):\n"
indent not greater e.g. at tab sizes 1, 2</pre>
</div>
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<div class="section" id="using-within-your-program">
<h2>Using within Your Program<a class="headerlink" href="#using-within-your-program" title="Permalink to this headline">¶</a></h2>
<p>As soon as I discovered the mistake in my Queue example, I decided I
needed to add an automatic check to my PyMOTW build process. I
created a <tt class="docutils literal"><span class="pre">tabcheck</span></tt> task in my <tt class="docutils literal"><span class="pre">pavement.py</span></tt> build script so I
could run <cite>paver tabcheck</cite> and scan the code I’m working on for
PyMOTW. This is possible because tabnanny exposes its <cite>check()</cite>
function as a public API.</p>
<p>Here’s an example of using tabnanny that doesn’t require understanding
Paver’s task definition decorators.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">sys</span>
<span class="kn">import</span> <span class="nn">tabnanny</span>
<span class="c"># Turn on verbose mode</span>
<span class="n">tabnanny</span><span class="o">.</span><span class="n">verbose</span> <span class="o">=</span> <span class="mi">1</span>
<span class="k">for</span> <span class="n">dirname</span> <span class="ow">in</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">tabnanny</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="n">dirname</span><span class="p">)</span>
</pre></div>
</div>
<p>And in action:</p>
<div class="highlight-python"><pre>$ python tabnanny_check.py ../Queue
'../Queue': listing directory
'../Queue/__init__.py': Clean bill of health.
'../Queue/feedparser.py': Clean bill of health.
'../Queue/fetch_podcasts.py': *** Line 78: trouble in tab city! ***
offending line: "\t\tfor enclosure in entry.get('enclosures', []):\n"
indent not greater e.g. at tab sizes 1, 2</pre>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you run these examples against the PyMOTW code it won’t report
the same errors, since I have fixed my code in this release.</p>
</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/tabnanny.html">tabnanny</a></dt>
<dd>The standard library documentation for this module.</dd>
<dt><tt class="xref py py-mod docutils literal"><span class="pre">tokenize</span></tt></dt>
<dd>Lexical scanner for Python source code.</dd>
</dl>
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