Returns a :class:`list` of :class:`Roles` that have been overridden from
        their default values in the :attr:`Guild.roles` attribute.

def changed_roles(self):
        """Returns a :class:`list` of :class:`Roles` that have been overridden from
        their default values in the :attr:`Guild.roles` attribute."""
        ret = []
        g = self.guild
        for overwrite in filter(lambda o: o.type == 'role', self._overwrites):
            role = g.get_role(overwrite.id)
            if role is None:
                continue

            role = copy.copy(role)
            role.permissions.handle_overwrite(overwrite.allow, overwrite.deny)
            ret.append(role)
        return ret