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<qhelp>

<overview>

<p>

When an instance of a class is initialized, the super-class state should be

fully initialized before it becomes visible to the subclass.

Calling methods of the subclass in the superclass' <code>__init__</code>

method violates this important invariant.

</p>

</overview>

<recommendation>

<p>Do not use methods that are subclassed in the construction of an object.

For simpler cases move the initialization into the superclass' <code>__init__</code> method,

preventing it being overridden. Additional initialization of subclass should

be done in the <code>__init__</code> method of the subclass.

For more complex cases, it is advisable to use a static method or function to manage

object creation.

</p>

<p>Alternatively, avoid inheritance altogether using composition instead.</p>

</recommendation>

<example>

<sample src="InitCallsSubclassMethod.py" />

</example>

<references>

<li>CERT Secure Coding: <a href="https://www.securecoding.cert.org/confluence/display/java/MET05-J.+Ensure+that+constructors+do+not+call+overridable+methods">

Rule MET05-J</a>. Although this is a Java rule it applies to most object-oriented languages.</li>

<li>Python Standard Library: <a href="http://docs.python.org/library/functions.html#staticmethod">Static methods</a>.</li>

<li>Wikipedia: <a href="http://en.wikipedia.org/wiki/Composition_over_inheritance">Composition over inheritance</a>.</li>

</references>

</qhelp>