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<div><h1 id="a0000000041">6.12 Assertions</h1>
<p> <a name="a0000000603" id="a0000000603"></a> </p><p>The <tt class="tt">assert</tt> command<a name="a0000000604" id="a0000000604"></a> can be used to assert that a logical expression, such as <tt class="tt">x>0</tt>, is true. An error is reported if the expression is false, and optionally a string can be supplied to provide a more informative error message to the user: </p><pre>
assert x>0
assert y<0 "y must be less than zero."
</pre><p>The <tt class="tt">assert</tt> command<a name="a0000000605" id="a0000000605"></a> can also be used to test the version number of PyXPlot. It is possible to test either that the version is newer than or equal to a specific version, using the <tt class="tt"><img src="images/img-0035.png" alt="$>$" style="vertical-align:0px;
width:12px;
height:11px" class="math gen" />=</tt> operator, or that it is older than a specific version, using the <tt class="tt"><img src="images/img-0034.png" alt="$<$" style="vertical-align:0px;
width:12px;
height:11px" class="math gen" /></tt> operator, as demonstrated in the following examples: </p><pre>
assert version >= 0.8.2
assert version < 0.8 "This script is designed for PyXPlot 0.7"
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