Class attributes can only be accessed via class type objects

gistfile1.py

class ClassAttribute(object):
    """Class attributes can only be accessed via class type objects.

    Attempting to access the attribute via an instance of the class will
    result in an AttributeError.
    """

    __slots__ = ('attr',)

    def __init__(self, attr):
        self.attr = attr

    def __get__(self, instance, type=None):
        if instance is not None:
            raise AttributeError("Attribute is not accessible via %s instances"
                    % type.__name__)
        return self.attr