Peter Otten <__pete...@web.de> wrote:
> kkumer wrote:
>
>>
>> I have to merge two dictionaries into one, and in
>> a "shallow" way: changing items should be possible
>> by operating either on two parents or on a
>> new dictionary. I am open to suggestions how
>> to do this (values are always numbers, BTW), but
>> I tried to do it by creating a dict-like class that just
>> forwards all calls to the two parent dicts, see below.
>>
>> It works, but one important thing is missing. I
>> am not able to expand new dictionary with
>> double-star operator ** to use it as a
>> set of keyword arguments of a function.
>> I googled a bit, but was unable to find what
>> property must an object have to be correctly
>> treated by **.
>
> The following experiment shows that you only need to implement a keys() and
> __getitem__() method.
>
> $ cat kw.py
> class A(object):
> def keys(self): return list("ab")
> def __getitem__(self, key):
> return 42
>
> def f(**kw):
> print(kw)
>
> f(**A())
> $ python kw.py
> {'a': 42, 'b': 42}
>
> However, if you have A inherit from dict...
>
> $ cat kwd.py
> class A(dict):
> def keys(self): return list("ab")
> def __getitem__(self, key):
> return 42
>
> def f(**kw):
> print(kw)
>
> f(**A())
> $ python kwd.py
> {}
>
> it stops working -- probably a side-effect of some optimization.
> So if you change your hubDict's base class from dict to object you should
> get the desired behaviour.
>
> Peter
--
Kresimir Kumericki http://www.phy.hr/~kkumer/
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