[Python-ideas] Allow using ** twice

[Zachary Ware]

On Thu, Jun 6, 2013 at 10:05 AM, Oscar Benjamin
<oscar.j.benjamin at gmail.com> wrote:
> On 6 June 2013 15:54, Markus Unterwaditzer <markus at unterwaditzer.net> wrote:
>> This indicates for me that it generally should be possible to generate the union of two dicts with sth like {} + {}.
>
> It cannot be a union since the dicts can have different values
> correspond to the same keys.
>
> However you can make a class that will try several mappings sequentially e.g.:
>
> class MapJoin:
>     def __init__(self, *mappings):
>         self.mappings = mappings
>     def __getitem__(self, key):
>         for mapping in self.mappings:
>             try:
>                 return mapping[key]
>             except KeyError:
>                 pass
>         else:
>             raise KeyError(str(key))
>     # Perhaps other mapping methods here...
>
> Then you can do:
>
> func(**MapJoin(map1, map2))
>

That sounds rather like collections.ChainMap.