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
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