[issue15870] PyType_FromSpec should take metaclass as an argument

[Petr Viktorin]

Petr Viktorin <encukou at gmail.com> added the comment:

> 2. Use eval from C to create the class with a metaclass, eg.
>      class Foo(metaclass=MessageMeta)

You can also call (PyObject_Call*) the metaclass with (name, bases, namespace); this should produce a class. Or not:

    >>> class Foo(metaclass=print):
    ...     def foo(self): pass
    ... 
    Foo () {'__module__': '__main__', '__qualname__': 'Foo', 'foo': <function Foo.foo at 0x7f6e9ddd9e50>}

PyType_FromSpecEx will surely need to limit the metaclass to subtypes of type. What other limitations are there? How closely can we approach the behavior of the `class` statement in Python?


> 3. Manually set FooType->ob_type = &MetaType

I wouldn't recommend doing that after PyType_Ready is called. Including indirectly, which the type-creation functions in the stable ABI do.

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nosy: +petr.viktorin

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<https://bugs.python.org/issue15870>
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