Python中[ ]、[:]和[::]的用法总结

#!/usr/bin/env python
# -*- coding: utf-8 -*-
 
from __future__ import absolute_import
from __future__ import print_function
from __future__ import division
 
import os
import sys
import cv2
import numpy as np
import matplotlib.pyplot as plt
 
print(16 * "++--")
 
str_list = ['A', 'B', 'C', 'D', 'E', 'F', 'G']
print("str_list:", str_list)
print("str_list[3]:", str_list[3])
print("str_list[1:4]:", str_list[1:4])
print("str_list[:4]:", str_list[:4])
print("str_list[4:]:", str_list[4:])
print("str_list[::-1]:", str_list[::-1])
print("str_list[::2]:", str_list[::2])
---------------------------------------------------
 
++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--
str_list: ['A', 'B', 'C', 'D', 'E', 'F', 'G']
str_list[3]: D
str_list[1:4]: ['B', 'C', 'D']
str_list[:4]: ['A', 'B', 'C', 'D']
str_list[4:]: ['E', 'F', 'G']
str_list[::-1]: ['G', 'F', 'E', 'D', 'C', 'B', 'A']
str_list[::2]: ['A', 'C', 'E', 'G']
 
Process finished with exit code 0

import os
import sys
import cv2
import numpy as np
print(16 * "++--")
str_data = 'abcdefg'
print("str_data[3]:", str_data[3])
print("str_data[3:5]:", str_data[3:5])
print("str_data[:5]:", str_data[:5])
print("str_data[3:]:", str_data[3:])
print("str_data[::2]:", str_data[::2])
print("str_data[::-1]:", str_data[::-1])
print("str_data[-1]:", str_data[-1])
print("str_data[-2]:", str_data[-2])
print("str_data[-5:-2]:", str_data[-5:-2])
print("str_data[-2:-5]:", str_data[-2:-5])
--------------------------------------------------
++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--
str_data[3]: d
str_data[3:5]: de
str_data[:5]: abcde
str_data[3:]: defg
str_data[::2]: aceg
str_data[::-1]: gfedcba
str_data[-1]: g
str_data[-2]: f
str_data[-5:-2]: cde
str_data[-2:-5]: 
Process finished with exit code 0