[Python-Dev] collections module (original) (raw)

Martin v. Loewis martin at v.loewis.de
Sat Jan 10 17:35:16 EST 2004

Robert Brewer wrote:

This seems a bit too easy to do "as needed" to warrant a new builtin, but that's why we have proposals, I guess:

class DefaultingDict(dict): def init(self, default): self.default = default def getitem(self, key): return self.get(key, self.default())

It would not necessarily have to be a builtin, but it should be part of the standard library somewhere. Having to write it anew everytime you need it is too tedious, so I usually have a try:except: block, doing the defaulting in the except: part.

There would be also more semantic issues, such as whether has_key should always return True on a DefaultingDict. Your implementation is incomplete, too - .pop() should invoke the default function, as should .get().

Regards, Martin

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