classmethods, class variables and subclassing

[Andrew Jaffe]

Steven Bethard wrote:
> Andrew Jaffe wrote:
> 
> I'm not sure if I understand your goal here, but you can get different 
> behavior using super().
> 
> py> class sup(object):
> ...     cvar1 = None
> ...     cvar2 = None
> ...     @classmethod
> ...     def setcvar1(cls, val):
> ...         cls.cvar1 = val
> ...     @classmethod
> ...     def setcvar2(cls, val):
> ...         cls.cvar2 = val
> ...     @classmethod
> ...     def printcvars(cls):
> ...         print cls.cvar1, cls.cvar2
> ...
> py> class sub(sup):
> ...     cvar1a = None
> ...     @classmethod
> ...     def setcvar1(cls, val, vala):
> ...         cls.cvar1a = vala
> ...         super(sub, cls).setcvar1(val)
> ...     @classmethod
> ...     def printcvars(cls):
> ...         print cls.cvar1a
> ...         super(sub, cls).printcvars()
> ...
> py> sub.setcvar1(1, 10); sub.setcvar2(2); sub.printcvars()
> 10
> 1 2
> py> sup.printcvars()
> None None

Aha! This is the behavior I want -- the variables get set correctly when 
the methods are called on the subclass. I thought super() might be the 
right idea, but I didn't realize you could call it as super(sub, cls) 
rather than with an instance in the second slot. I don't think my use 
case ever needs the superclass to have the variables accessible as in 
your next ideas, not reproduced here.

Thanks!

Andrew