Python 语法
数组索引
a[start:end] # items start through end-1
a[start:] # items start through the rest of the array
a[:end] # items from the beginning through end-1
a[:] # a copy of the whole array
a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items
a[::stride] # [a[0], a[stride], …, a[-1]]
a[low::stride] # [a[low], a[low+stride], …, a[-1]]
a[:high:stride] # [a[0], a[stride], …, a[high-1]]
a[low:high:stride] # [a[low], a[low+stride], …, a[high-1]]
a[::-stride] # [a[-1], a[-1-stride], …, a[0]]
a[high::-stride] # [a[high], a[high-stride], …, a[0]]
a[:low:-stride] # [a[-1], a[-1-stride], …, a[low+1]]
a[high:low:-stride] # [a[high], a[high-stride], …, a[low+1]]