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
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