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Date: Mon, 25 Jul 2011 22:44:17 -0400
From: Victor Khangulov <kilka.hamsa@gmail.com>
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To: python list <python-list@python.org>
Subject: Re: Trying to learn about metaclasses
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10319

Hi Steven,

I too am just learning about metaclasses in Python and I found the 
example you posted to be excellent.

I played around with it and noticed that the issue seems to be the 
double-underscore in front of the fields (cls.__fields = {}).  If you 
change this parameter to use the single-underscore, the code works 
perfectly.

I think that because of the double-underscore, the name of the attribute 
"fields" gets mangled by the interpreter and is not inherited from the 
parent class in its accessible form.  Now, I am not sure if the code 
posted uses an earlier version of Python where these rule are different 
or if there is a more correct way to achieve this.  I will follow this 
discussion to see if someone has a better answer.

-victor