2010/11/4 Stefan Behnel <[email protected]>:
> Stefan Behnel, 04.11.2010 14:17:
>> BTW, I'll ask on python-dev about the way __build_class__ works here.
>
> ;) writing e-mails about a problem without sending them away is the best
> way to understand the topic.
>
> Ok, so, __build_class__ is actually ok, because it *is* the point where the
> class body is evaluated. So, __prepare__ is really called before the
> evaluation of the body (which is done in a "function" call near the end)
> and the metaclass is called afterwards.
>
> We could essentially do the same thing in Cython. At the point where the
> class dict is now getting instantiated, we need to put the code of the
> first part of __build_class__, i.e. look up the metaclass from the keywords
> and find and call its __prepare__ method. Then, evaluate the class body
> into the class namespace object that __prepare__ returned, followed by the
> call to __Pyx_CreateClass().
>
> If we don't find a metaclass in the keywords, we do not support __prepare__
> but try to look up the __metaclass__ field in the class namespace during
> __Pyx_CreateClass().
>
> Stefan
>
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I have attached patch (in trac) for python3 metaclass support,
__prepare__ now works this way:
if metaclass is defined py3 way and it has __prepare__, namespace is
merged into dict.
This is wrong but it's much easy to implement, right behavior could be
imlemented later.
This could be done this way:
1. PyClassDefNode detect that class definition is py3 style and has
metaclass keyword defined, it sets some flag
2. then code generation should work this way:
name = <class name>
bases = <tuple of bases>
metaclass = <metaclass>
mkw = <metaclass keywords dict>
if hasattr(metaclass, '__prepare__'):
dict = __Pyx_PrepareClass(metaclass, bases, name, mkw)
else:
dict = {}
# now fill dict with attributes
margs = tuple(name, bases, dict)
klass = PyEval_CallObjectWithKeywords(metaclass, margs, mkw)
This is interesting to implement, I'll try...
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