Example
a = range(10)
a [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
a[2] 2
a[-2] 8
a[2:] [ 2, 3, 4, 5, 6, 7, 8, 9]
a[:2] [0, 1 ]
a[2:6] [ 2, 3, 4, 5 ]
a[2:-2] [ 2, 3, 4, 5, 6, 7 ]
a[-6:-2] [ 4, 5, 6, 7 ]
a[:] [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
a[::2] [0, 2, 4, 6, 8 ]
a[2::2] [ 2, 4, 6, 8 ]
a[:6:2] [0, 2, 4 ]
a[2:6:2] [ 2, 4 ]
a[::-1] [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]