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<div class="yui-g" id="internals-contributing-writing-code-coding-style">
<div class="section" id="s-coding-style">
<span id="coding-style"></span><h1>Coding style<a class="headerlink" href="#coding-style" title="Permalink to this headline">¶</a></h1>
<p>Please follow these coding standards when writing code for inclusion in Django.</p>
<div class="section" id="s-python-style">
<span id="python-style"></span><h2>Python style<a class="headerlink" href="#python-style" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Unless otherwise specified, follow <span class="target" id="index-0"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a>.</p>
<p>You could use a tool like <a class="reference external" href="http://pypi.python.org/pypi/pep8">pep8</a> to check for some problems in this
area, but remember that <span class="target" id="index-1"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a> is only a guide, so respect the style of
the surrounding code as a primary goal.</p>
<p>One big exception to <span class="target" id="index-2"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a> is our preference of longer line lengths.
We’re well into the 21st Century, and we have high-resolution computer
screens that can fit way more than 79 characters on a screen. Don’t limit
lines of code to 79 characters if it means the code looks significantly
uglier or is harder to read.</p>
</li>
<li><p class="first">Use four spaces for indentation.</p>
</li>
<li><p class="first">Use underscores, not camelCase, for variable, function and method names
(i.e. <tt class="docutils literal"><span class="pre">poll.get_unique_voters()</span></tt>, not <tt class="docutils literal"><span class="pre">poll.getUniqueVoters</span></tt>).</p>
</li>
<li><p class="first">Use <tt class="docutils literal"><span class="pre">InitialCaps</span></tt> for class names (or for factory functions that
return classes).</p>
</li>
<li><p class="first">In docstrings, use “action words” such as:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
<span class="sd">"""</span>
<span class="sd"> Calculates something and returns the result.</span>
<span class="sd"> """</span>
<span class="k">pass</span>
</pre></div>
</div>
<p>Here’s an example of what not to do:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
<span class="sd">"""</span>
<span class="sd"> Calculate something and return the result.</span>
<span class="sd"> """</span>
<span class="k">pass</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="s-template-style">
<span id="template-style"></span><h2>Template style<a class="headerlink" href="#template-style" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">In Django template code, put one (and only one) space between the curly
brackets and the tag contents.</p>
<p>Do this:</p>
<div class="highlight-html+django"><div class="highlight"><pre><span class="cp">{{</span> <span class="nv">foo</span> <span class="cp">}}</span>
</pre></div>
</div>
<p>Don’t do this:</p>
<div class="highlight-html+django"><div class="highlight"><pre><span class="cp">{{</span><span class="nv">foo</span><span class="cp">}}</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="s-view-style">
<span id="view-style"></span><h2>View style<a class="headerlink" href="#view-style" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">In Django views, the first parameter in a view function should be called
<tt class="docutils literal"><span class="pre">request</span></tt>.</p>
<p>Do this:</p>
<div class="highlight-python"><pre>def my_view(request, foo):
# ...</pre>
</div>
<p>Don’t do this:</p>
<div class="highlight-python"><pre>def my_view(req, foo):
# ...</pre>
</div>
</li>
</ul>
</div>
<div class="section" id="s-model-style">
<span id="model-style"></span><h2>Model style<a class="headerlink" href="#model-style" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Field names should be all lowercase, using underscores instead of
camelCase.</p>
<p>Do this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Person</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">first_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="n">last_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
</pre></div>
</div>
<p>Don’t do this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Person</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">FirstName</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="n">Last_Name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">The <tt class="docutils literal"><span class="pre">class</span> <span class="pre">Meta</span></tt> should appear <em>after</em> the fields are defined, with
a single blank line separating the fields and the class definition.</p>
<p>Do this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Person</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">first_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="n">last_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Meta</span><span class="p">:</span>
<span class="n">verbose_name_plural</span> <span class="o">=</span> <span class="s">'people'</span>
</pre></div>
</div>
<p>Don’t do this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Person</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">first_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="n">last_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Meta</span><span class="p">:</span>
<span class="n">verbose_name_plural</span> <span class="o">=</span> <span class="s">'people'</span>
</pre></div>
</div>
<p>Don’t do this, either:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Person</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="k">class</span> <span class="nc">Meta</span><span class="p">:</span>
<span class="n">verbose_name_plural</span> <span class="o">=</span> <span class="s">'people'</span>
<span class="n">first_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">20</span><span class="p">)</span>
<span class="n">last_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">The order of model inner classes and standard methods should be as
follows (noting that these are not all required):</p>
<ul class="simple">
<li>All database fields</li>
<li>Custom manager attributes</li>
<li><tt class="docutils literal"><span class="pre">class</span> <span class="pre">Meta</span></tt></li>
<li><tt class="docutils literal"><span class="pre">def</span> <span class="pre">__unicode__()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">def</span> <span class="pre">__str__()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">def</span> <span class="pre">save()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">def</span> <span class="pre">get_absolute_url()</span></tt></li>
<li>Any custom methods</li>
</ul>
</li>
<li><p class="first">If <tt class="docutils literal"><span class="pre">choices</span></tt> is defined for a given model field, define the choices as
a tuple of tuples, with an all-uppercase name, either near the top of
the model module or just above the model class. Example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">GENDER_CHOICES</span> <span class="o">=</span> <span class="p">(</span>
<span class="p">(</span><span class="s">'M'</span><span class="p">,</span> <span class="s">'Male'</span><span class="p">),</span>
<span class="p">(</span><span class="s">'F'</span><span class="p">,</span> <span class="s">'Female'</span><span class="p">),</span>
<span class="p">)</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="s-use-of-django-conf-settings">
<span id="use-of-django-conf-settings"></span><h2>Use of <tt class="docutils literal"><span class="pre">django.conf.settings</span></tt><a class="headerlink" href="#use-of-django-conf-settings" title="Permalink to this headline">¶</a></h2>
<p>Modules should not in general use settings stored in <tt class="docutils literal"><span class="pre">django.conf.settings</span></tt>
at the top level (i.e. evaluated when the module is imported). The explanation
for this is as follows:</p>
<p>Manual configuration of settings (i.e. not relying on the
<tt class="docutils literal"><span class="pre">DJANGO_SETTINGS_MODULE</span></tt> environment variable) is allowed and possible as
follows:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.conf</span> <span class="kn">import</span> <span class="n">settings</span>
<span class="n">settings</span><span class="o">.</span><span class="n">configure</span><span class="p">({},</span> <span class="n">SOME_SETTING</span><span class="o">=</span><span class="s">'foo'</span><span class="p">)</span>
</pre></div>
</div>
<p>However, if any setting is accessed before the <tt class="docutils literal"><span class="pre">settings.configure</span></tt> line,
this will not work. (Internally, <tt class="docutils literal"><span class="pre">settings</span></tt> is a <tt class="docutils literal"><span class="pre">LazyObject</span></tt> which
configures itself automatically when the settings are accessed if it has not
already been configured).</p>
<p>So, if there is a module containing some code as follows:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.conf</span> <span class="kn">import</span> <span class="n">settings</span>
<span class="kn">from</span> <span class="nn">django.core.urlresolvers</span> <span class="kn">import</span> <span class="n">get_callable</span>
<span class="n">default_foo_view</span> <span class="o">=</span> <span class="n">get_callable</span><span class="p">(</span><span class="n">settings</span><span class="o">.</span><span class="n">FOO_VIEW</span><span class="p">)</span>
</pre></div>
</div>
<p>...then importing this module will cause the settings object to be configured.
That means that the ability for third parties to import the module at the top
level is incompatible with the ability to configure the settings object
manually, or makes it very difficult in some circumstances.</p>
<p>Instead of the above code, a level of laziness or indirection must be used, such
as <tt class="xref py py-class docutils literal"><span class="pre">django.utils.functional.LazyObject</span></tt>,
<tt class="xref py py-func docutils literal"><span class="pre">django.utils.functional.lazy()</span></tt> or <tt class="docutils literal"><span class="pre">lambda</span></tt>.</p>
</div>
<div class="section" id="s-miscellaneous">
<span id="miscellaneous"></span><h2>Miscellaneous<a class="headerlink" href="#miscellaneous" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>Mark all strings for internationalization; see the <a class="reference internal" href="../../../topics/i18n/index.html"><em>i18n
documentation</em></a> for details.</li>
<li>Remove <tt class="docutils literal"><span class="pre">import</span></tt> statements that are no longer used when you change code.
The most common tools for this task are <a class="reference external" href="http://pypi.python.org/pypi/pyflakes">pyflakes</a> and <a class="reference external" href="http://pypi.python.org/pypi/pylint">pylint</a>.</li>
<li>Systematically remove all trailing whitespaces from your code as those
add unnecessary bytes, add visual clutter to the patches and can also
occasionally cause unnecessary merge conflicts. Some IDE’s can be
configured to automatically remove them and most VCS tools can be set to
highlight them in diff outputs. Note, however, that patches which only
remove whitespace (or only make changes for nominal <span class="target" id="index-3"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a> conformance)
are likely to be rejected, since they only introduce noise rather than
code improvement. Tidy up when you’re next changing code in the area.</li>
<li>Please don’t put your name in the code you contribute. Our policy is to
keep contributors’ names in the <tt class="docutils literal"><span class="pre">AUTHORS</span></tt> file distributed with Django
– not scattered throughout the codebase itself. Feel free to include a
change to the <tt class="docutils literal"><span class="pre">AUTHORS</span></tt> file in your patch if you make more than a
single trivial change.</li>
</ul>
</div>
</div>
</div>
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<h3><a href="../../../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Coding style</a><ul>
<li><a class="reference internal" href="#python-style">Python style</a></li>
<li><a class="reference internal" href="#template-style">Template style</a></li>
<li><a class="reference internal" href="#view-style">View style</a></li>
<li><a class="reference internal" href="#model-style">Model style</a></li>
<li><a class="reference internal" href="#use-of-django-conf-settings">Use of <tt class="docutils literal"><span class="pre">django.conf.settings</span></tt></a></li>
<li><a class="reference internal" href="#miscellaneous">Miscellaneous</a></li>
</ul>
</li>
</ul>
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