[Python-ideas] Syntax for allowing extra keys when unpacking a dict as keyword arguments

[Eric V. Smith]

On 4/12/2019 1:52 PM, Viktor Roytman wrote:
> That is an interesting solution. In the case of a function from another 
> library, you could apply the decorator as needed like.
> 
>      fief(func)(**{'a': 1, 'b': 2})
> 
> It looks a little strange, but I've seen stranger.

Indeed. That's not so bad, and I'll look into using fief.

And this is definitely better (for various values of "better") than 
language syntax to achieve the same thing.

Eric

> 
> On Friday, April 12, 2019 at 12:18:34 PM UTC-4, Lucas Bourneuf wrote:
> 
>     Hello !
> 
>     I made *fief*, a small python package allowing just that using a
>     decorator:
> 
>          from fief import filter_effective_parameters as fief
> 
>          @fief
>          def func(a, b):
>              # some implementation
> 
>          # and then, use it as you want to:
>          func(**MY_BIG_CONFIG_DICT_WITH_MANY_WEIRD_KEYS)
> 
>     The code is quite simple. You may want to use it, with modifications
>     (i didn't touch the code for months, maybe years ; it could probably
>     be improved now).
>     Link: https://github.com/aluriak/fief <https://github.com/aluriak/fief>
> 
>     The code:
> 
>     def filter_effective_parameters(func):
>          """Decorator that filter out parameters in kwargs that are not
>     related to
>          any formal parameter of the given function.
>          """
>          @wraps(func)
>          def wrapper(*args, **kwargs):
>              formal_parameters =
>     frozenset(signature(func).parameters.keys())
>              return func(*args, **{
>                  arg: value
>                  for arg, value in kwargs.items()
>                  if arg in formal_parameters
>              })
>          return wrapper
> 
>     Best regards,
>     --lucas
> 
> 
> 
>     ----- Mail original -----
>      > De: "Viktor Roytman" <viktor... at gmail.com <javascript:>>
>      > À: "python-ideas" <python... at googlegroups.com <javascript:>>
>      > Envoyé: Vendredi 12 Avril 2019 18:01:43
>      > Objet: Re: [Python-ideas] Syntax for allowing extra keys when
>     unpacking a dict as keyword arguments
> 
>      > I could see this being an option, but to someone unfamiliar with
>     it, it
>      > might seem strange that * unpacks iterables, ** unpacks dicts,
>     and *** is a
>      > special thing only for keyword arguments that mostly behaves like
>     **.
>      >
>      > On Friday, April 12, 2019 at 11:26:37 AM UTC-4, Bruce Leban wrote:
>      >>
>      >>
>      >> On Fri, Apr 12, 2019, 8:12 AM Viktor Roytman <viktor... at gmail.com
>      >> <javascript:> wrote:
>      >>
>      >>>
>      >>>     >>> func(**{'a': 1, 'b': 2})
>      >>>     Traceback (most recent call last):
>      >>>       File "<stdin>", line 1, in <module>
>      >>>     TypeError: func() got an unexpected keyword argument 'b'
>      >>>
>      >>
>      >> Perhaps func(***kws)?
>      >>
>      >> I think this is a real problem given the frequent convention
>     that you can
>      >> freely add fields to json objects with the additional fields to
>     be ignored.
>      >>
>      >
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