<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p> When you compare an object to <code>None</code>, use <code>is</code> rather than <code>==</code>.

<code>None</code> is a singleton object, comparing using <code>==</code> invokes the <code>__eq__</code>

method on the object in question, which may be slower than identity comparison. Comparing to

<code>None</code> using the <code>is</code> operator is also easier for other programmers to read.</p>

</overview>

<recommendation>

<p>Replace <code>==</code> with <code>is</code>.</p>

</recommendation>

<example>

<p>The <code>filter2</code> function is likely to be more efficient than the <code>filter1</code>

function because it uses an identity comparison.</p>

<sample src="EqualsNone.py" />

</example>

<references>

<li>Python Language Reference: <a href="http://docs.python.org/reference/expressions.html#is">Comparisons</a>,

<a href="http://docs.python.org/reference/datamodel.html#object.__eq__">object.__eq__</a>.</li>

</references>

</qhelp>