On Jun 3, 10:11 pm, Matthew Wilson <[EMAIL PROTECTED]> wrote:
> I used defaultdict.fromkeys to make a new defaultdict instance, but I
> was surprised by behavior:
>
> >>> b = defaultdict.fromkeys(['x', 'y'], list)
>
> >>> b
> defaultdict(None, {'y': <type 'list'>, 'x': <type 'list'>})
>
> >>> b['x']
> <type 'list'>
>
> >>> b['z']
> ------------------------------------------------------------
> Traceback (most recent call last):
> File "<ipython console>", line 1, in <module>
> KeyError: 'z'
>
> I think that what is really going on is that fromdict makes a regular
> dictionary, and then hands it off to the defaultdict class.
>
> I find this confusing, because now I have a defaultdict that raises a
> KeyError.
>
> Do other people find this intuitive?
>
> Would it be better if defaultdict.fromkeys raised a
> NotImplementedException?
>
> Or would it be better to redefine how defaultdict.fromkeys works, so
> that it first creates the defaultdict, and then goes through the keys?
>
> All comments welcome. If I get some positive feedback, I'm going to try
> to submit a patch.
>
> Matt
To me it's intuitive for it to raise a KeyError, afterall the Key
isn't in the dictionary.
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