python列表各種切片姿勢

 順着切，反着切，想怎么切就怎么切，但是別被坑。

mylist = [1,2,3,4,5,6,7,8,9]
print(mylist[2:7:2]) # [3, 5, 7]
print(mylist[:7:2]) # [1, 3, 5, 7]
print(mylist[2::2]) # [3, 5, 7, 9]
print(mylist[2:9:2]) # [3, 5, 7, 9]
print(mylist[2:10:2]) # [3, 5, 7, 9]
print(mylist[::2]) # [1, 3, 5, 7, 9]
print(mylist[7:2:2]) # []
print(mylist[2:7:-2]) # []
print(mylist[7:2:-2]) # [8, 6, 4]
print('============')
print(mylist[-2:-7:-2]) # [8, 6, 4]
print(mylist[:-7:-2]) # [9, 7, 5]
print(mylist[-2::-2]) # [8, 6, 4, 2]
print(mylist[-2:-10:-2]) # [8, 6, 4, 2]
print(mylist[::-2]) # [9, 7, 5, 3, 1]
print(mylist[-7:-2:-2]) # []
print(mylist[-2:-7:2]) # []
print(mylist[-7:-2:2]) # [3, 5, 7]

　

步長如果是整數，開始要小於結束，否則結果肯定為空
步長如果是負數，開始要大於結束，否則結果肯定為空 

 

# 反轉
print(mylist[::-1]) # [9, 8, 7, 6, 5, 4, 3, 2, 1]
mylist.reverse()
print(mylist) # [9, 8, 7, 6, 5, 4, 3, 2, 1]

　

左閉右開

print([1,2,3,4,5,6,7,8,9][1:3:])  # [2, 3]
print([1,2,3,4,5,6,7,8,9][-1:-7:-1])  # [9, 8, 7, 6, 5, 4]