Idiom gone, or did it really ever exist? () is ()

[Duncan Booth]

"Mike C. Fletcher" <mcfletch at home.com> wrote in
<mailman.987578846.15784.python-list at python.org>: 

> You want this kind of construct when creating "generic services" that
> can process any object type (including None), so need to be able to
> determine whether the object passed is, in fact, the value None, or
> merely the absence of a value.
> 
> 
So why not use the portable and safe way of finding out whether your 
function was called with a particular argument or not?
   def foo(**kw):
       validargs = { 'bar': None }
       validargs.update(kw)
       assert len(validargs)==1

       if kw.has_key('bar'):
           print "Have bar"
       else:
           print "No bar"

-- 
Duncan Booth                                             
duncan at dales.rmplc.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?