[Tutor] creating variables at runtime

[Lloyd Kvam]

I believe you are right about creating specific dictionaries to support this.  I went to
the trouble of creating a list to avoid checking every __getattr__ key argument against
globals().  Using a dictionary to provide both the check and the function reference makes
a lot of sense.

Thank you very much!

Jeff Shannon wrote:

>>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
> 
> 
> 
> _______________________________________________
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
> 
> 


-- 
Lloyd Kvam
Venix Corp.
1 Court Street, Suite 378
Lebanon, NH 03766-1358

voice: 
603-443-6155
fax: 
801-459-9582