[Python-Dev] dict.addlist() (original) (raw)

Phillip J. Eby pje at telecommunity.com
Tue Jan 20 09:56:57 EST 2004

At 09:26 AM 1/20/04 -0500, Bob Ippolito wrote:

There are other reasons to use setdefault. This one is pretty common though, but I think a more generic solution could be implemented.

Perhaps: d.setdefault(k, factory=list).append(v) ?

+100. :) An excellent replacement for my recurring use of:

try: return self._somemapping[key] except: self._somemapping[key] = value = somethingExpensive(key) return value

That becomes simply:

 return self._somemapping.setdefault(
     key, factory=lambda: somethingExpensive(key)
 )

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