a complement function

[Tim Hochberg]

Brad Knotwell <knotwell at ix.netcom.com> writes:

> Hello all--
> 
> I was wondering if there's a clean way to do the following:
> 
> def complement(function):
>     return lambda x,function=function: not apply(function,x)
> 
> print complement(lambda x: x == 1)((1,))
> print complement(lambda x: x == 1)((2,))
> print complement(lambda x,y: x == y)((3,4))
> print complement(lambda x,y: x == y)((4,4))
> 
> 
> As you can see, it works fine as long as the function is called with
> a tuple representing all arguments.  What I'd prefer is the more obvious
> interface:
> 
> print complement(lambda x: x == 1)(1)
> print complement(lambda x: x == 1)(2)
> print complement(lambda x,y: x == y)(3,4)
> print complement(lambda x,y: x == y)(4,4)
> 
> FWIW, I suppose the real question would ask if there's any way for
> default arguments and variably-sized argument lists to play nicely
> together.

I think your best bet here is to migrate from a real function to a
class pretending it's a function. That tends to be helpful when
default arguments start causing problems. For example:

class complement:
    def __init__(self, function):
        self.function = function
    def __call__(self, *args, **kargs):
        return apply(self.function, args, kargs)

print complement(lambda x: x == 1)(1)
print complement(lambda x: x == 1)(2)
print complement(lambda x,y: x == y)(3,4)
print complement(lambda x,y: x == y)(4,4)

Enjoy,

-tim