[Python-Dev] defaultdict and on_missing()
python at rcn.com
Wed Feb 22 17:20:44 CET 2006
[Guido van Rossum"]
> If we removed on_missing() from dict, we'd have to override
> __getitem__ in defaultdict (regardless of whether we give
>defaultdict an on_missing() hook or in-line it).
You have another option. Keep your current modifications to
dict.__getitem__ but do not include dict.on_missing(). Let it only
be called in a subclass IF it is defined; otherwise, raise KeyError.
That keeps me happy since the basic dict API won't show on_missing(),
but it still allows a user to attach an on_missing method to a dict subclass
or if needed. I think all your test cases would still pass without
This is approach is not much different than for other magic methods which
kick-in if defined or revert to a default behavior if not.
My core concern is to keep the dict API clean as a whistle.
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