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43 lines
1.6 KiB
XML
43 lines
1.6 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>If a class has a <code>close()</code> or similar method to release resources, then it
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should be made a context manager. Using a context manager allows instances of the class to be used
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in the <code>with</code> statement, improving code size and readability. This is a simpler and more
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reliable method than implementing just a <code>__del__</code> method.
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</p>
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</overview>
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<recommendation>
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<p>The context manager requires an <code>__enter__</code> and an <code>__exit__</code> method:</p>
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<ul>
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<li>
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<code>__enter__</code> method acquires the resource or does nothing if the resource
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is acquired in the <code>__init__</code> method</li>
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<li><code>__exit__</code> method releases the resource, this can just be a simple wrapper around the
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<code>close</code> method.</li>
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</ul>
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</recommendation>
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<example>
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<p>The following example shows how a class definition that implements <code>__del__</code> can be
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updated to use a context manager.</p>
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<sample src="ShouldBeContextManager.py" />
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</example>
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<references>
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<li>Effbot: <a href="https://web.archive.org/web/20201012110738/http://effbot.org/zone/python-with-statement.htm">Python with statement</a>.</li>
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<li>Python Standard Library: <a href="http://docs.python.org/library/stdtypes.html#context-manager-types">Context manager
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</a>.</li>
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<li>Python Language Reference: <a href="http://docs.python.org/2.7/reference/datamodel.html#with-statement-context-managers">
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With Statement Context Managers</a>.</li>
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<li>Python PEP 343: <a href="http://www.python.org/dev/peps/pep-0343">The "with" Statement</a>.</li>
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</references>
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</qhelp>
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