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POSetting a class' metaclass using a decorator
 

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    <p>Following <a href="https://stackoverflow.com/a/5121381/623518">this answer</a> it seems that a class' metaclass may be changed after the class has been defined by using the following*:</p> <pre><code>class MyMetaClass(type): # Metaclass magic... class A(object): pass A = MyMetaClass(A.__name__, A.__bases__, dict(A.__dict__)) </code></pre> <p>Defining a function</p> <pre><code>def metaclass_wrapper(cls): return MyMetaClass(cls.__name__, cls.__bases__, dict(cls.__dict__)) </code></pre> <p>allows me to apply a decorator to a class definition like so,</p> <pre><code>@metaclass_wrapper class B(object): pass </code></pre> <p>It seems that the metaclass magic is applied to <code>B</code>, however <code>B</code> has no <code>__metaclass__</code> attribute. Is the above method a sensible way to apply metaclasses to class definitions, even though I am definiting and re-definiting a class, or would I be better off simply writing</p> <pre><code>class B(object): __metaclass__ = MyMetaClass pass </code></pre> <p>I presume there are some differences between the two methods.</p> <hr> <p>*Note, the original answer in the linked question, <code>MyMetaClass(A.__name__, A.__bases__, A.__dict__)</code>, returns a <code>TypeError</code>:</p> <blockquote> <p>TypeError: type() argument 3 must be a dict, not dict_proxy</p> </blockquote> <p>It seems that the <code>__dict__</code> attribute of <code>A</code> (the class definition) has a type <code>dict_proxy</code>, whereas the type of the <code>__dict__</code> attribute of an <em>instance</em> of <code>A</code> has a type <code>dict</code>. Why is this? Is this a Python 2.x vs. 3.x difference?</p>
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