[Tutor] creating variables at runtime

[Jeff Shannon]

> Lloyd Kvam <pythontutor@venix.com> wrote:

>
> I've been using globals() in kind of the reverse way to create class instances based
> on the desired class name, sort of a quick Class Factory Method.
>         instance = globals()['Classname']()

Actually, this is much closer to the "right" way to use globals(), I think.  I know that
the corresponding locals() function returns a dictionary that should be considered
read-only (effects of altering it are undefined), and my gut reaction is to try to treat
globals() the same way (though, admittedly, I don't see a similar warning about globas()
in the docs).  Then again, in almost any case where something like this might be useful,
I'd prefer to create a dictionary and just use that.  For instance, in your sample code...



> class Site(Table):
>         fk_obj_list = ['Reservation','Siteprice']
> class Siteprice(Table):
> class Reservation(Table):

I'd do this as:

class Siteprice(Table):
class Reservation(Table):

class Site(Table):
    fk_objects = { 'Reservation': Reservation, 'Siteprice': Siteprice }

and then when I needed to create the class, I could do

        if key in self.fk_objects.keys():
            obj = self.fk_objects[key]()

Of  course, this may just be my personal style, and YMMV and all, but I think that this is
more explicit, and cleaner, than using globals().

Jeff Shannon
Technician/Programmer
Credit International