[Python-Dev] Proposal: defaultdict

Raymond Hettinger raymond.hettinger at verizon.net
Sun Feb 19 08:11:33 CET 2006

[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 

Is the notion of __contains__ at odds with notion of universality?


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