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39 lines
1.6 KiB
XML
39 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>When a file is opened, it should always be closed.
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</p>
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<p>A file opened for writing that is not closed when the application exits may result in data loss, where not all of the data written may be saved to the file.
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A file opened for reading or writing that is not closed may also use up file descriptors, which is a resource leak that in long running applications could lead to a failure to open additional files.
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</p>
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</overview>
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<recommendation>
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<p>Ensure that opened files are always closed, including when an exception could be raised.
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The best practice is often to use a <code>with</code> statement to automatically clean up resources.
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Otherwise, ensure that <code>.close()</code> is called in a <code>try...except</code> or <code>try...finally</code>
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block to handle any possible exceptions.
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</p>
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</recommendation>
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<example>
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<p>In the following examples, in the case marked BAD, the file may not be closed if an exception is raised. In the cases marked GOOD, the file is always closed.</p>
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<sample src="examples/FileNotAlwaysClosed.py" />
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</example>
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<references>
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<li>Python Documentation: <a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files">Reading and writing files</a>.</li>
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<li>Python Language Reference: <a href="http://docs.python.org/reference/compound_stmts.html#the-with-statement">The with statement</a>,
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<a href="http://docs.python.org/reference/compound_stmts.html#the-try-statement">The try statement</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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