StackOverflow2013

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19252704
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2013-10-08T16:01:04.547
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2013-10-08T17:20:15.173
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2017-05-23T12:00:35.847
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19252588
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4
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text
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<p>Pythonic ways for checking for <code>None</code> or <code>null</code> are:</p> <pre><code>if element: # This is not null if not element: # This is null </code></pre> <p>There is a very <a href="https://stackoverflow.com/a/100762/1401034">detailed answer</a> on the difference between <code>if not x</code> and <code>if x == None</code>.</p> <h2>Edit 1:</h2> <p>Combining the comment and the other answers:</p> <h3>False Values</h3> <p>Python treats the following as <code>False</code> <a href="http://docs.python.org/2/library/stdtypes.html#truth-value-testing" rel="nofollow noreferrer">source</a>:</p> <ul> <li><code>None</code></li> <li><code>False</code></li> <li>zero of any numeric type, eg: <code>0</code>, <code>0L</code>, <code>0.0</code>, <code>0j</code></li> <li>any empty sequence, eg: <code>''</code>, <code>()</code>, <code>[]</code></li> <li>any empty mapping, eg: <code>{}</code></li> <li>instances of user-defined classes, if the class defines a <code>__nonzero__()</code> or<code>__len__()</code> method, when that method returns the integer <code>zero</code> or bool value <code>False</code></li> </ul> <h3>True Values</h3> <p>All other values are considered to be <code>True</code>.</p> <h3>Your question:</h3> <p>If you are indeed checking if <code>None</code> is present in your list (<code>[1,2,None,4,5,6]</code>) then @Poke 's answer is right:</p> <pre><code>>>> lst = [1, 2, None, 4, 5, 6] >>> None in lst True </code></pre> <p>If you are wanting to check that the element is <em>only</em> <code>None</code> then @esauro is correct in the comments:</p> <pre><code>>>> lst = [1, 2, None, 4, 5, 6] >>> for x in lst: ... if not x: ... print(x) None </code></pre> <p>But if your <code>lst</code> contains <code>0</code> (lst = [0, 1, 2, 4, 5, 6]) then your output will be <code>0</code>.</p> <p>The only way you could get round this would be to explicitly check <code>if element is None</code>or <code>if element is not None</code>. </p>
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