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35 lines
1.0 KiB
XML
35 lines
1.0 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p> When you compare an object to <code>None</code>, use <code>is</code> rather than <code>==</code>.
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<code>None</code> is a singleton object, comparing using <code>==</code> invokes the <code>__eq__</code>
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method on the object in question, which may be slower than identity comparison. Comparing to
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<code>None</code> using the <code>is</code> operator is also easier for other programmers to read.</p>
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</overview>
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<recommendation>
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<p>Replace <code>==</code> with <code>is</code>.</p>
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</recommendation>
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<example>
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<p>The <code>filter2</code> function is likely to be more efficient than the <code>filter1</code>
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function because it uses an identity comparison.</p>
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<sample src="EqualsNone.py" />
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</example>
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<references>
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<li>Python Language Reference: <a href="http://docs.python.org/reference/expressions.html#is">Comparisons</a>,
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<a href="http://docs.python.org/reference/datamodel.html#object.__eq__">object.__eq__</a>.</li>
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</references>
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</qhelp>
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