python class that acts as mapping for **unpacking -

without subclassing dict, class need considered mapping can passed method **

from abc import abcmeta  class uobj:     __metaclass__ = abcmeta  uobj.register(dict)  def f(**k): return k  o = uobj() f(**o)  # outputs: f() argument after ** must mapping, not uobj 

at least point throws errors of missing functionality of mapping, can begin implementing.

i reviewed emulating container types defining magic methods has no effect, , using abcmeta override , register dict validates assertions subclass, fails isinstance(o, dict). ideally, dont want use abcmeta.

the __getitem__() , keys() methods suffice:

>>> class d:         def keys(self):             return ['a', 'b']         def __getitem__(self, key):             return key.upper()   >>> def f(**kwds):         print kwds   >>> f(**d()) {'a': 'a', 'b': 'b'}