<!DOCTYPE qhelp PUBLIC

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

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<qhelp>

<overview>

<p>All code defined in assert statements is ignored when optimization is

requested, that is, the program is run with the <code>-O</code> flag.

If an assert statement has any side-effects then the behavior of

the program changes when optimization is requested.</p>

</overview>

<recommendation>

<p>Move all expressions with side-effects out of assert statements.</p>

</recommendation>

<example>

<p>

In the example, the exit code from <code>subprocess.call()</code> is checked against 0, but the entire

expression is called from within an <code>assert</code> statement. If the code is ever run, then the

not only the assertion itself, but also the external call, will be discarded. It is better to save the result

of <code>subprocess.call()</code> to a temporary variable, and to assert that variable to be 0.

</p>

<sample src="SideEffectInAssert.py" />

</example>

<references>

<li>Python Language Reference: <a href="http://docs.python.org/2/reference/simple_stmts.html#assert">The assert statement</a>.</li>

<li>TutorialsPoint, Python Programming: <a href="http://www.tutorialspoint.com/python/assertions_in_python.htm">Assertions in Python</a>.</li>

</references>

</qhelp>