[Python-Dev] Proposal: defaultdict (original) (raw)

Raymond Hettinger python at rcn.com
Sun Feb 19 04:53:35 CET 2006

> Also, I think haskey/in should return True if there is a default.

It certainly seems desirable to see True where d[somekey] doesn't raise an exception, but one could argue either way.

Some things can be agreed by everyone:

if contains always returns True, then it is a useless feature (since scripts containing a line such as "if k in dd" can always eliminate that line without affecting the algorithm).
if defaultdicts are supposed to be drop-in dict substitutes, then having contains always return True will violate basic dict invariants: del d[some_key] assert some_key not in d

Raymond