Ternary plus

Carl Banks pavlovevidence at gmail.com
Tue Feb 9 03:46:05 CET 2010


On Feb 8, 12:59 pm, Martin Drautzburg <Martin.Drautzb... at web.de>
wrote:
> Just for the hell of it ...
>
> I can easily define __plus__() with three parameters. If the last one is
> optional the + operation works as expected. Is there a way to pass the
> third argument to "+"

If, for some reason, you wanted to define a type for which it makes
sense to "add" three objects, but not two, you can get the effect you
want, kind of.

(a + b + c) is useful
(a + b) is meaningless

You can have __add__ return a closure for the first addition, then
perform the operation on the second one.  Example (untested):

class Closure(object):
    def __init__(self,t1,t2):
        self.t1 = t1
        self.t2 = t2
    def __add__(self,t3):
        # whole operation peformed here
        return self.t1 + self.t2 + t3

class MySpecialInt(int):
    def __add__(self,other):
        return Closure(self,other)


I wouldn't recommend it.  Just use a function call with three
arguments.


Carl Banks



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