Noissue - Document best practice for formatting multiline statements in Python

pages/coding-style.html

 title=Coding Style
 
 
 <h2 id="precedence">{{s1 Precedence}}</h2>
 
 <p>{{s2 The Adblock Plus coding style is based on others. Our rules (both general and language specific) always overrule referenced style guides. The language specific sections overrule the general section.}}</p>
 
 <h2 id="consistency">{{s3 Consistency}}</h2>
 
 <p>{{s4 Consistency is most important: Be consistent within functions, files, modules and projects. Making existing code conform with this style guide is fine, but it should happen in dedicated commits, preferably for a whole module or project at once.}}</p>
@@ skipping 47 matching lines @@
 <h2 id="python">{{s19 Python}}</h2>
 <ul>
   <li>{{python-general Follow <a href="https://www.python.org/dev/peps/pep-0008/"><fix>PEP-8</fix></a> and the recommendations in the offical <fix>Python</fix> documentation.}}</li>
   <li>{{python-version Make the code compatible with both <fix>Python 2.7</fix> and <fix>Python 3.5+</fix> (see <a href="https://docs.python.org/dev/howto/pyporting.html">this guide</a>). Use <a href="https://docs.python.org/2/library/__future__.html"><fix>__future__</fix> imports</a> to address syntactic differences but avoid <a href="https://pythonhosted.org/six/"><fix>six</fix></a>, <a href="http://python-future.org/compatible_idioms.html"><fix>python-future</fix></a>, etc. to not introduce additional dependencies.}}</li>
   <li>{{python-strings Write string literals so that they match the behaviour of <a href="https://docs.python.org/3/library/functions.html#ascii"><code><fix>ascii()</fix></code></a>, i.e. use single quotes except to avoid escaping of embedded quotes and use <code><fix>\u</fix></code> escapes for non-ascii characters but don't prefix strings with <code><fix>u</fix></code>. For docstrings, however, follow <a href="https://www.python.org/dev/peps/pep-0257/">PEP-257</a>.}}</li>
   <li>{{python-prefix In modules, prefix private functions and variables with a single underscore.}}</li>
   <li>{{python-concatenation Use the <code><fix>+</fix></code> operator when concatenating exactly two strings, use the <a href="https://docs.python.org/2/library/stdtypes.html#str.format"><code><fix>format()</fix></code> method</a> for more complex string formatting, use the <a href="https://docs.python.org/2/library/stdtypes.html#str.join"><code><fix>join()</fix></code> method</a> when concatenating pre-existing sequences.}}</li>
   <li>{{python-tuple-vs-list Use tuples for data that have structure, use lists for data that have order.}}</li>
   <li>{{python-builtins Don't override builtins except for <a href="https://docs.python.org/2/library/functions.html#non-essential-built-in-funcs">non-essential builtins</a> and <code><fix>file</fix></code> which is superfluos in modern code as well.}}</li>
   <li>{{python-map-filter Use list comprehensions or generator expressions instead of calling <code><fix>map()</fix></code> or <code><fix>filter()</fix></code> with a lambda function.}}</li>
+  <li>{{python-multiline The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. Long lines can be broken over multiple lines by wrapping expressions in parentheses:}}
+    <ol>
+      <li>{{python-multiline-a1[list item] aligning follow up lines with the opening parentheses and putting the closing parentheses at the end of the last line}}
+          (<a onclick="getElementById('python-multiline-a1-example').classList.toggle('hide');">{{python-multiline-a1-example example}}</a>), or
+        <pre class="hide" id="python-multiline-a1-example">
+    long_object_name.long_method_name(argument1, argument2,
+                                      keyword_argument=value)
+
+    very_long_variable = ['a list of', 'strings that does not',
+                          'fit into', 'one line']
+        </pre>
+      </li>
+      <li>{{python-multiline-a2[list item] breaking the line at the opening parentheses, indenting follow up lines by 4 spaces, and placing the closing parentheses on a separate line that is aligned with the line that contains the opening parentheses}}
+          (<a onclick="getElementById('python-multiline-a2-example').classList.toggle('hide');">{{python-multiline-a2-example example}}</a>).
+        <pre class="hide" id="python-multiline-a2-example">
+    long_object_name.long_method_name(
+        argument1,
+        argument2,
+        keyword_argument=value,
+    )
+
+    very_long_variable = [
+        'a list of',
+        'strings that does not',
+        'fit into',
+        'one line',
+    ]
+        </pre>
+      </li>
+    </ol>
+    {{python-multiline-commas When breaking lists of items separated by commas (e.g. lists, dicts, argument lists) using the second approach add a comma after the last element. This allows adding and rearranging items without touching unrelated lines.}}
+  </li>
   <li>{{python-regexp Use <a href="https://docs.python.org/2/library/re.html#re.search"><code><fix>re.search()</fix></code></a> instead of <code><fix>re.match()</fix></code> to avoid <a href="https://docs.python.org/2/library/re.html#search-vs-match">confusion</a> about implied beginning of the string but not the ending.}}</li>
   <li>
     {{python-flake8 Run <a href="https://pypi.python.org/pypi/flake8"><fix>flake8</fix></a> with following extensions and fix all reported errors:}}
     <ul>
       <li><a href="https://hg.adblockplus.org/codingtools/file/tip/flake8-eyeo">flake8-eyeo</a></li>
       <li><a href="https://pypi.python.org/pypi/flake8-docstrings">flake8-docstrings</a> ({{python-flake8-docstring-exception with <code><fix>D1</fix></code> ignored}})</li>
       <li><a href="https://pypi.python.org/pypi/pep8-naming">pep8-naming</a></li>
     </ul>
   </li>
   <li>{{python-tests Write tests and have them run along <fix>flake8</fix> using <a href="https://pypi.python.org/pypi/tox"><fix>tox</fix></a>.}}</li>
@@ skipping 18 matching lines @@
 <ul>
   <li>{{objc-conventions Follow Apple's <a href="https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Conventions/Conventions.html">conventions</a>}}.</li>
 </ul>
 
 <h2 id="puppet">{{s31 Puppet}}</h2>
 <ul>
   <li>{{s32 Follow the <a href="http://docs.puppetlabs.com/guides/style_guide.html">Puppet Style Guide</a>.}}</li>
   <li>{{s33 Opening braces don't go on their own line.}}</li>
   <li>{{s34 Arrows should not be aligned.}}</li>
 </ul>