[Tutor] Re: Python vs. Ruby

[Abel Daniel]

Gregor Lingl writes:
> On the other hand there are types of objects, e.g. type 'function',
> which cannot be subclassed as far as I know (and regret).
>
> Testtask: is it possible to subclass (numerical)  functions - say this
> new class is named Fun - e.g. by adding a __add__ method, in a
> way that their instances can be added, like:
>  >>> from math import sin, cos
>  >>> f = Fun(sin) + Fun(cos)   ### see remark below
>  >>> f(1)
> #### should output sin(1)+cos(1)
> In short: it would be nice to create some sort of function algebra.
>
> In Python this seems a bit weird because of the special
> way functions are defined (namely via the reserved word def).
> So how should (or could) one define a "fun"? Maybe by making
> it "callable" somehow? (Oh, I feel that this is not a very sharply
> defined problem ...)
Well, here is a shot at it:

class Fun:
    def __init__(self, func):
        self.func=func
    
    def __call__(self, *a, **kw):
        return self.func(*a, **kw)

    def __add__(self, other):
        def f(*a, **kw):
            return self.func(*a, **kw) + other(*a, **kw)
        return Fun(f)

>>> from math import sin, cos
>>> fc=Fun(cos)
>>> fs=Fun(sin)
>>> fcs=fc+fs
>>> fc(1)+fs(1)
1.3817732906760363
>>> fcs(1)
1.3817732906760363
>>> 

Finishing up (adding other stuff from
http://python.org/doc/current/ref/numeric-types.html
and handling things like "Fun(math.sin) + 5" ) are left as an exercise
to the reader. :)

Of course Fun instances won't be functions, but the interface is the same
(they can be called), so it shouldn't matter.

-- 
Abel Daniel