Why does built-in set not take keyword arguments?

[Jack Diederich]

On Thu, May 04, 2006 at 02:08:30PM -0400, Steven Watanabe wrote:
> I'm trying to do something like this in Python 2.4.3:
> 
> class NamedSet(set):
>   def __init__(self, items=(), name=''):
>     set.__init__(self, items)
>     self.name = name
> 
> class NamedList(list):
>   def __init__(self, items=(), name=''):
>     list.__init__(self, items)
>     self.name = name
> 
> I can do:
> 
> >>> mylist = NamedList(name='foo')
> 
> but I can't do:
> 
> >>> myset = NamedSet(name='bar')
> TypeError: set() does not take keyword arguments
> 
> How come? How would I achieve what I'm trying to do?

setobject.c checks for keyword arguments in it's __new__ instead 
of its __init__.  I can't think of a good reason other to enforce
inheriters to be maximally set-like.  We're all adults here so 
I'd call it a bug.  bufferobect, rangeobject, and sliceobject all 
do this too, but classmethod and staticmethod both check in tp_init.
Go figure.

As a work around use a function to make the set-alike.

class NamedSet(set): pass

def make_namedset(vals, name):
  ob = NamedSet(vals)
  ob.name = name
  return ob

Then make_namedset as a constructor in place of NamedSet(vals, name)

-Jack