FileNotAlwaysClosed.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>

<overview>
<p>When a file is opened, it should always be closed. 
</p>
<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.
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. 
</p>
</overview>
<recommendation>

<p>Ensure that opened files are always closed, including when an exception could be raised.
The best practice is often to use a <code>with</code> statement to automatically clean up resources.
Otherwise, ensure that <code>.close()</code> is called in a <code>try...except</code> or <code>try...finally</code> 
block to handle any possible exceptions.
</p>

</recommendation>
<example>
<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>

<sample src="examples/FileNotAlwaysClosed.py" />

</example>
<references>

<li>Python Documentation: <a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files">Reading and writing files</a>.</li>
<li>Python Language Reference: <a href="http://docs.python.org/reference/compound_stmts.html#the-with-statement">The with statement</a>,
 <a href="http://docs.python.org/reference/compound_stmts.html#the-try-statement">The try statement</a>.</li>
<li>Python PEP 343: <a href="http://www.python.org/dev/peps/pep-0343">The "with" Statement</a>.</li>



</references>
</qhelp>