Variable arguments (*args, **kwargs): seeking elegance
Peter Otten
__peter__ at web.de
Sun Oct 6 03:25:51 EDT 2013
John Ladasky wrote:
> Hi folks,
>
> I'm trying to make some of Python class definitions behave like the ones I
> find in professional packages, such as Matplotlib. A Matplotlib class can
> often have a very large number of arguments -- some of which may be
> optional, some of which will assume default values if the user does not
> override them, etc.
Personally, I'd rather not copy that kind of interface.
> I have working code which does this kind of thing. I define required
> arguments and their default values as a class attribute, in an
> OrderedDict, so that I can match up defaults, in order, with *args. I'm
> using set.issuperset() to see if an argument passed in **kwargs conflicts
> with one which was passed in *args. I use set.isdisjoint() to look for
> arguments in **kwargs which are not expected by the class definition,
> raising an error if such arguments are found.
Why do you rely on a homebrew solution instead of actually calling the
function or initializer?
> Even though my code works, I'm finding it to be a bit clunky. And now,
> I'm writing a new class which has subclasses, and so actually keeps the
> "extra" kwargs instead of raising an error... This is causing me to
> re-evaluate my original code.
>
> It also leads me to ask: is there a CLEAN and BROADLY-APPLICABLE way for
> handling the *args/**kwargs/default values shuffle that I can study? Or
> is this sort of thing too idiosyncratic for there to be a general method?
>
> Thanks for any pointers!
inspect.getcallargs() may be worth a look.
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