Is there a method like '__getattribute__' for class (not instance) variables?

Question

I have a class sysprops in which I'd like to have a number of constants. However, I'd like to pull the values for those constants from the database, so I'd like some sort of hook any time one of these class constants are accessed (something like the getattribute method for instance variables).

class sysprops(object):
    SOME_CONSTANT = 'SOME_VALUE'

sysprops.SOME_CONSTANT  # this statement would not return 'SOME_VALUE' but instead a dynamic value pulled from the database.

Answer 1

While the other two answers have a valid method. I like to take the route of 'least-magic'.

You can do something similar to the metaclass approach without actually using them. Simply by using a decorator.

def instancer(cls):
    return cls()

@instancer
class SysProps(object):
    def __getattribute__(self, key):
        return key # dummy

This will create an instance of SysProps and then assign it back to the SysProps name. Effectively shadowing the actual class definition and allowing a constant instance.

Since decorators are more common in Python I find this way easier to grasp for other people that have to read your code.

Answer 2

Although I think it is a very bad idea to do this, it is possible:

class GetAttributeMetaClass(type):
    def __getattribute__(self, key):
        print 'Getting attribute', key

class sysprops(object):
    __metaclass__ = GetAttributeMetaClass