IncorrectlyOverriddenMethod.qhelp

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


<overview>
<p> There is a call to the overridden method, and potentially the overriding method,
with arguments that are not legal for the overriding method.
This will cause an error if the overriding method is called and is a
violation of the Liskov substitution principle.
</p>

</overview>
<recommendation>

<p>Ensure that the overriding method accepts all the parameters that are legal for the
overridden method.</p>

</recommendation>
<example>
<p>In this example there is a mismatch between the legal parameters for the base 
class method <code>(self, source, filename, symbol)</code> and the extension method 
<code>(self, source)</code>. The extension method can be used to override the base 
method as long as values are not specified for the <code>filename</code> and (optional)
<code>symbol</code> parameters. If the extension method was passed the additional 
parameters accepted by the base method then an error would occur.</p>

<sample src="SignatureIncorrectlyOverriddenMethod.py" />

<p>The extension method should be updated to support the <code>filename</code> and 
<code>symbol</code> parameters supported by the overridden method.</p>

</example>
<references>

<li>Wikipedia: <a href="http://en.wikipedia.org/wiki/Liskov_substitution_principle">Liskov Substitution Principle</a>, <a href="http://en.wikipedia.org/wiki/Method_overriding#Python">Method overriding</a>.</li>


</references>
</qhelp>