[issue38315] Provide defaultdict variant that passes key to default_factory

wang xuancong added the comment: I agree with Mark Amery. The reason why defaultdict still exists given that everything can be achieved by subclassing the built-in dict is because of convenience. I suggest maybe Python developer can put it into low priority instead. -- nosy: +xuancon

[issue38315] Provide defaultdict variant that passes key to default_factory

Mark Amery added the comment: I'm aware of __missing__. However, I don't think its existence is by itself a knockdown argument against doing this. __missing__ also fulfils the need satisfied by defaultdict, yet Python still has both - and the latter is almost always more convenient to use wh

[issue38315] Provide defaultdict variant that passes key to default_factory

Raymond Hettinger added the comment: The __missing__() method already fulfills this need: class DoubleDict(dict): def __missing__(self, key): return key * 2 If desired, it can also add entries: class DoubleDict(dict): def __missing__(self, key): se

[issue38315] Provide defaultdict variant that passes key to default_factory

New submission from Mark Amery : There seems to be at least some demand for the ability to have the key being accessed be passed to the factory function of a defaultdict. See e.g. https://stackoverflow.com/q/2912231/1709587 (13k views) or previous enhancement suggestion https://bugs.python.or