def sorted(self, attrname, reverse=False):
        attrs = []
        for i, pseudo in self:
            try:
                a = getattr(pseudo, attrname)
            except AttributeError:
                a = np.inf
            attrs.append((i, a))
        return self.__class__([self[a[0]] for a in sorted(attrs, key=lambda t: t[1], reverse=reverse)])