[docs] [issue18334] type(name, bases, dict) does not call metaclass' __prepare__ attribute

Nick Coghlan report at bugs.python.org
Mon Jul 1 04:00:51 CEST 2013

Nick Coghlan added the comment:

I think we should actually go further, and explicitly defer to http://docs.python.org/3/library/types#dynamic-type-creation for dynamic type creation.

Type shouldn't be called with arbitrary bases any more, precisely *because* doing so breaks __prepare__ handling. It's only safe to call a metaclass directly with arbitrary bases if you call types.prepare_class first:

    mcl, namespace, kwds = types.prepare_class(name, bases)
    cls = mcl(name, bases, namespace, **kwds)

You can only skip types.prepare_class if you *know* you already have the right metaclass (such as when there aren't any base classes defined).


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