Python 2.7.6: Affected
Python 3.2.3: Not affected

dict() allows keyword expansion using a dict() with integer keys, whereas attempting to do so with most other functions raises a TypeError with the message, "keywords must be strings". The same thing happens with collections.defaultdict(), but not collections.Counter() or collections.OrderedDict, presumably because they override dict.__init__().

>>> old_dict = {'a': 1, 2: 'b'}
>>> old_dict
{'a': 1, 2: 'b'}
>>> other_dict = {'c': 3, 4: 'd'}
>>> other_dict
>>> new_dict = dict(old_dict, **other_dict)
>>> new_dict
{'a': 1, 2: 'b', 4: 'd', 'c': 3}

I feel like this must be known, but I didn't find anything with a search.

2.7 can't be changed for backward compatibility reasons, and python3 enforces the restriction in dict, as you observe.

I don't know if a python2 documentation note is worthwhile, but given the conversations at pycon about adding additional -3 warnings to 2.7, it seems like this is a place such a warning would be justified.

IIRC, we've only created -3 warnings for things that would be incorrectly accepted by Python 3 (such as floor division using /).   

I don't think that applies here and isn't worth monkeying with Py2.7.  It goes in the harmless nuisance category, something that affects almost no one.

I agree with Raymond: this isn't a practical problem worth solving. If it's causing an actual problem, please re-open this issue and give a use case.

Thanks.

I'm not going to reopen it, but my point was that if we really are going to add additional -3 warnings to help people port 2.7, as discussed at the language summit, then this would be a candidate.