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Sorry if I have to use you as Google, but Google does not help. I was looking for a very good tutorial about metaclasses in Python. One feature I remember about it was a three-paned image where you had metaclasses, classes and instances, one for each column of the image. The author progressively added blocks for each of them, while explaining the magic behind metaclasses.
It was a very good tutorial but I really cannot find it any more.
You may be referring to Python Types and Objects.