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POCannot inherit from multiple classes defining __slots__?
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  1. POCannot inherit from multiple classes defining __slots__?
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    copied!<p>A certain situation in Python recently alarmed me, and its reason is still not completely clear after a little research. The following class definitions appear to working flawlessly and will produce what is intended:</p> <pre><code>class A: __slots__ = 'a', 'b' class B(A): __slots__ = () class C(A): __slots__ = () class D(B, C): __slots__ = () </code></pre> <p>There are four classes arranged in a diamond inheritance pattern. However, a somewhat similar pattern is not allowed. The following class definitions seem as though they are functioning the same as the first:</p> <pre><code>class B: __slots__ = 'a', 'b' class C: __slots__ = 'a', 'b' class D(B, C): __slots__ = () Traceback (most recent call last): File "&lt;pyshell#74&gt;", line 1, in &lt;module&gt; class D(B, C): __slots__ = () TypeError: multiple bases have instance lay-out conflict </code></pre> <p>However, a <code>TypeError</code> is raised in this example. So three questions arise: (1) Is this a bug in Python, considering the slot names? (2) What would justify such an answer? (3) <em>What is the best workaround?</em></p> <hr> <p><strong>References:</strong></p> <ul> <li><a href="http://mail.python.org/pipermail/python-list/2002-December/740850.html">__slots__ and multiple inheritance</a> (with replies following)</li> <li><a href="http://bytes.com/topic/python/answers/576995-multiple-inheritance-__slots__">Multiple inheritance and __slots__</a></li> <li><a href="https://groups.google.com/group/comp.lang.python/msg/0f2e859b9c002b28">Don't use __slots__</a></li> <li><a href="http://www.velocityreviews.com/forums/t339645-multiple-inheritance-__slots__-problem.html">Multiple Inheritance __slots__ problem</a></li> </ul>
 

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