Getting a class attribute

[Johann Hibschman]

Alex  writes:

>> It is possible to get the class atribute "a" in the default function
>> parameter?

> My understanding is that the default values are computed at compile
> time, so not really.  Perhaps you could redefine the function each time
> the member 'a' changes?  Here is an example.  It does not really make
> new_degree_sin4 into a class method, as I don't know how.  I am pretty
> sure it's possible and desirable to do so, though.  Hopefully someone
> else will tell you.

AFAIK, you would have to make the function a *class* variable.
i.e. change


> import math

> class Eg:

>     def __init__ (self):
>         self.set_factor (1)

>     def set_factor (self, a):
>         self.a = a
>         def new_degree_sin4 (deg, factor=(a*(math.pi/180)),
>                              sin=math.sin):
>             return sin (deg * factor)
>         self.new_degree_sin4 = new_degree_sin4

to

def set_factor(self, a):
    self.a = a
    # i.e. now I include self in the method signature
    def new_degree_sin4(self, deg, factor=(a*(math.pi/180)), sin=math.sin):
        return sin (deg * factor)
    # and set the value in the class, not the instance
    Eg.new_degree_sin4 = new_degree_sin4

> if __name__ == '__main__':
>     eg = Eg ()
>     print eg.new_degree_sin4 (5)
>     eg.set_factor (6)
>     print eg.new_degree_sin4 (5)

That lets you get access to "self", but at the cost of rewriting the
class method itself.  Hm.  Now that I think about it, this seems like
a Really Bad Idea, since if you had multiple instances, you'd be
overwriting the same class method each time.

Maybe someone more wizardly than I can answer this.  Just don't say
"metaclass" three times, or you'll summon a Horror.

-- 
Johann Hibschman                           johann at physics.berkeley.edu