Sort list of lists ascending and then descending [duplicate]

L = [['a',1], ['a',2], ['a',3], ['b',1], ['b',2], ['b',3]]
L.sort(key=lambda k: (k[0], -k[1]), reverse=True)

L now contains:

[['b', 1], ['b', 2], ['b', 3], ['a', 1], ['a', 2], ['a', 3]]