[Python-ideas] Thoughts on "extended mapping unpacking"

[Neil Girdhar]

On Thu, May 24, 2018 at 8:00 AM Serhiy Storchaka <storchaka at gmail.com>
wrote:

> 24.05.18 11:38, Neil Girdhar пише:
> > I was previously constructing an object like this:
> >
> > tb = TemporalBehavior(**kwargs, **parameters)
> >
> > where various subclasses were doing things like
> >
> > def __init__(self, some_kwarg, some_other_kwargs, some_parameter,
> > some_other_parameter):
> >
> > Then I realized that I want to pass the paramters as a dictionary so
> > that I can store it..  I changed the code to this:
> >
> > def __init__(self, some_kwarg, some_other_kwargs, parameters):
> >
> > but I still need "some_parameter", so I did
> >
> > some_parmeter = parameters['some_parameter']
> > some_other_parmeter = parameters['some_other_parameter']
> >
> > Great, but now I have to check that exactly the list of parameters that
> > I need is being sent in, so I need to do something like
> >
> > if set(parameters) != ('some_parameter', 'some_other_parameter'):
> >      raise ValueError
> >
> > It might be nice to do instead
> >
> > {'some_parameter': p, 'some_other_parameter': q} = parameters
>
> p = parameters.pop('some_parameter')
> q = parameters.pop('some_other_parameter')
> if parameters:
>      raise ValueError
>
> parameters is a Mapping subclass and I don't want to destroy it

> or
>
> p, q = (lambda some_parameter, some_other_parameter: some_parameter,
> some_other_parameter)(**parameters)
>
> that works

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