>>> xs = {'a': 4, 'b': 3, 'c': 2, 'd': 1}
>>> {k: v for k, v in sorted(xs.items(), key=lambda item: item[1])}
# {'d': 1, 'c': 2, 'b': 3, 'a': 4}
или
>>> dict(sorted(xs.items(), key=lambda item: item[1]))