Question about collections.defaultdict

Robert Kern robert.kern at
Mon Mar 26 15:44:51 CEST 2012

On 3/26/12 2:33 PM, Steven W. Orr wrote:
> I created a new class called CaseInsensitiveDict (by stealing from code I found
> on the web, thank you very much). The new class inherits from dict. It makes it
> so that if the key has a 'lower' method, it will always access the key using lower
> I'd like to change the place where I previously declared a dict
> self.lookup = defaultdict(list)
> so that the new code will allow this new dict to be used instead. But then I
> realized I may have painted myself into a small corner:
> Is there a way to use defaultdict so that I can override what *kind* of dict it
> will use?


> I would like the value to still be a list be default, but it seems like I can't
> tell defaultdict to use *my* new dict.
> Do I give up on defaultdict?

Assuming that your CaseInsensitiveDict subclasses from dict or UserDict, it's 
relatively easy to make a subclass of your CaseInsensitiveDict act like a 
defaultdict. Just implement the __missing__(key) method appropriately (and 
modify the constructor to take the callable, of course).

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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