"Raymond Hettinger" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > [Terry Reedy] >> One is a 'universal dict' that maps every key to something -- the >> default if >> nothing else. That should not have the default ever explicitly entered. >> Udict.keys() should only give the keys *not* mapped to the universal >> value. > > Would you consider it a mapping invariant that "k in dd" implies "k in > dd.keys()"? > > Is the notion of __contains__ at odds with notion of universality?
No and not sure. I'll leave it to Martin v. Löwis to explain/defend his particular notion of a udict. My main point is that there are multiple legitimate variations of the notion of a default dict, so that there is no 'one right way' to design one. I notice that Michael Urman and Ian Bicking said much the same today. Of course, having said that different variations are useful in different situations, I would nowise claim that all variations can serve as drop-in replacements for regular dicts everywhere they are now used. I think that a new default-dict feature should cater to such variations. Beyond that, I don't know whether it is better to modify dict (with blank hooks) or add a new subclassable default-dict base type. Terry Jan Reedy
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