'inverting' a dict

sdd daniels at dsl-only.net
Thu Jan 1 23:31:01 CET 2004


Bob van der Poel wrote:
> This is sort of off topic for the thread, but I've got a similar 
> problem. In this case I have a dict like:
> 
>     { 'key1': 'value1', 'key2': value2}
> 
> and I sometimes need to find the key for the value. All values/keys are 
> unique. I just use a loop:
> 
>     for a in dict:
>         if dict[a]== targ:
>             return a
>     return None
For a few hunts, I'd do:
      for key,value in dictionary.iteritems():
          if value == target:
              return key
      return None

Of course, if it probed a lot between changes, it's better to

reversedictionary = dict([(v,k) for k,v in dictionary.items()])

-Scott David Daniels
Scott.Daniels at Acm.Org



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