Variable arguments (*args, **kwargs): seeking elegance
Peter Cacioppi
peter.cacioppi at gmail.com
Tue Oct 8 04:30:19 EDT 2013
On Saturday, October 5, 2013 9:04:25 PM UTC-7, John Ladasky wrote:
> Hi folks,
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> 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.
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> 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.
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> 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.
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> 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?
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> Thanks for any pointers!
"One thought -- often, people turn to subclassing as the only tool in
their toolbox. Have you considered that it may be easier/better to work
with delegation and composition instead? "
Double like.
Subclassing is awesome when it is used properly ... which usually means used cautiously.
Delegation/composition just doesn't result in the some sort of weird gotchas.
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