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The Metaclass Hook in Python 3

Метки: python

Python 3 changes the metaclass hook. It doesn’t disallow the __metaclass__ field, but it ignores it. Instead, you use a keyword argument in the base-class list:

class Simple1(object, metaclass = SimpleMeta1):
    ...

This means that none of the (clever) alternative ways of defining __metaclass__ directly as a class or function are available in Python 3 [[check this]]. All metaclasses must be defined as separate classes. This is probably just as well, as it makes metaclass programs more consistent and thus easier to read and understand.