Gavin Panella added the comment:
It's inconsistent that defaultdict([]) should be rejected:
>>> defaultdict([])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: first argument must be callable or None
but defaultdict.fromkeys([]) is okay:
>>> defaultdict.fromkeys([])
defaultdict(None, {})
The constructor signature differs between defaultdict and dict, and
defaultdict.fromkeys is an alternate constructor, so it seems reasonable to
also change its signature.
Also confusing is that I can call fromkeys on an instance of defaultdict:
>>> dd = defaultdict(list)
>>> dd.fromkeys([1])
defaultdict(None, {1: None})
Instinctively I expect the default_factory to be carried over, even though I
realise that would be odd behaviour for Python. If defaultdict.fromkeys were to
expect a mandatory default_factory argument there wouldn't be this moment of
confusion.
----------
nosy: +allenap
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<http://bugs.python.org/issue23372>
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