I want to create a class that behaves like collections.defaultdict, without having the usage code specify the factory. EG: instead of

class Config(collections.defaultdict):pass

this:

Config = functools.partial(collections.defaultdict, list)

This almost works, but

isinstance(Config(), Config)

fails. I am betting this clue means there are more devious problems deeper in also. So is there a way to actually achieve this?

I also tried:

class Config(Object):__init__ = functools.partial(collections.defaultdict, list)

I don't think there's a standard method to do it, but if you need it often, you can just put together your own small function:

import functools
import collectionsdef partialclass(cls, *args, **kwds):class NewCls(cls):__init__ = functools.partialmethod(cls.__init__, *args, **kwds)return NewClsif __name__ == '__main__':Config = partialclass(collections.defaultdict, list)assert isinstance(Config(), Config)