python常用小技巧
1.列表取值
（1）每次取3个
a = [1, 2, 3, 4, 5, 6, 7]
step = 3
for i in range(0, len(a), step):
print(a[i:i+step])打印结果：
[1, 2, 3]
[4, 5, 6]
[7]
a = [1, 2, 3, 4, 5, 6, 7]
step = 3
for i in range(0, len(a), step):
print(a[i:i+step])打印结果：
[1, 2, 3]
[4, 5, 6]
[7]