On Thu, Oct 4, 2018 at 10:58 AM Steven D'Aprano <steve@pearwood.info> wrote:
While keyword arguments have to be identifiers, using **kwargs allows arbitrary strings which aren't identifiers:
py> def spam(**kwargs): ... print(kwargs) ... py> spam(**{"something arbitrary": 1, '\n': 2}) {'something arbitrary': 1, '\n': 2}
There is some discussion on Python-Ideas on whether or not that behaviour ought to be considered a language feature, an accident of implementation, or a bug.
I would expect this to be costly/annoying for implementations to enforce, doing it at call time is probably too late to be efficient, it would need help from dicts themselves or even strings. A hack that currently works because of this is with dict itself:
d = {'a-1': 1, 'a-2': 2, 'a-3': 3} d1 = dict(d, **{'a-2': -2, 'a-1': -1}) d1 is d False d1 {'a-1': -1, 'a-2': -2, 'a-3': 3}