获取list或tuple的部分元素：

L = ['Michael', 'Sarah', 'Tracy', 'Bob', 'Jack']L[0:3]['Michael', 'Sarah', 'Tracy']L[:3]['Michael', 'Sarah', 'Tracy']L[-2:]['Bob', 'Jack']L[-2:-1]['Bob']L = list(range(100))L[0,1,2,3,4,5,...,99]L[:10:2][0,2,4,6,8]L[::5][0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]L[:][0, 1, 2, 3, ..., 99] //复制一个list(0,1,2,3)[:3](0,1,2)'ABCDEFG'[:3]'ABC''ABCDEFG'[::2]'ACEG'