[Django]-Python 2 and 3 metaclass compatibility when kwargs are used

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If I understand you right, there is no problem and it already works. Did you actually check whether your metaclass has the desired effect? Because I think it already does.

The class returned by with_metaclass is not meant to play the role of your class FooClass. It is a dummy class used as the base class of your class. Since this base class is of metaclass FooMeta, your derived class will also have metaclass FooMeta and so the metaclass will be called again with the appropriate arguments.

class FooMeta(type):
    def __new__(cls, name, bases, attrs):
        # do something with the kwargs...
        # for example:
        if 'foo' in attrs:
            attrs['fooattr'] = 'foovalue'
        return super(FooMeta, cls).__new__(cls, name, bases, attrs)
class FooBase(object):
    pass
class FooClass(with_metaclass(FooMeta, FooBase)):
    foo = "Yes"

>>> FooClass.fooattr
'foovalue'

Incidentally, it is confusing to call the third argument of your metaclass kwargs. It isn’t really keyword arguments. It is the __dict__ of the class to be created — that is, the class’s attributes and their values. In my experience this attribute is conventionally called attrs or perhaps dct (see e.g., here and here).

👤BrenBarn

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