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Thu Apr 19 17:04:12 EDT 2001 · http://mail.python.org/pipermail/python-list/2001-April/070392.html

"Delaney, Timothy" <tdelaney at avaya.com> writes:
> > > That is, I was attempting to distinguish between a call where
> > > argument is passed a NULL tuple and a call where argument is
> > > passed nothing at all.
> 
> # Should always work
> 
> class nullArgument:
>     """"""
> 
> __nullArgument = nullArgument()
> 
> def func (p=__nullArgument):
>     if p is __nullArgument:
>         print 'Default parameter'
>     else:
>         print 'Parameter passed'

When I first faced this problem, I started typing in code that was
equivalent to yours, until it occurred to me that there is no reason
to instantiate the class--the class itself serves as a fine default
argument.  In other words,

    class __nullArgument:
    	pass # Isn't this what pass is for?

    def func (p=__nullArgument):
    	if p is __nullArgument:
    	    print 'Default parameter'
    	else:
    	    print 'Parameter passed'

Cheers,
Michael

-- 
Michael Haggerty
mhagger at alum.mit.edu

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