Returns all documented class variables in the class, sorted
        alphabetically as a list of `pydoc.Variable`.

def class_variables(self):
        """
        Returns all documented class variables in the class, sorted
        alphabetically as a list of `pydoc.Variable`.
        """
        p = lambda o: isinstance(o, Variable) and self.module._docfilter(o)
        return filter(p, self.doc.values())