python3列表推导式

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1列表推导效率比传统的for 循环+append要快

code测试如下：

#传统的循环
import datetime
time1 = datetime.datetime.now()
list1 = []
for i in range(100000):
    if i%3==0:
        list1.append(i)
time2 = datetime.datetime.now()
print('cost_time1:',time2-time1)
#列表推倒
time3 = datetime.datetime.now()
list2=[i for i in range(100000) if i%2==0]
time4 = datetime.datetime.now()
print('cost_time2:',time4-time3)

多次打印的结果分别如下：

cost_time1: 0:00:00.016241
cost_time2: 0:00:00.011513
cost_time1: 0:00:00.016279
cost_time2: 0:00:00.011368
cost_time1: 0:00:00.017235
cost_time2: 0:00:00.011611

可以看出列表推导式不仅简洁，而且速度快了1/3左右。

2两次zip方法可以恢复原状

for i in zip([1,2,3],[4,5,6]):
    print(i)

(1, 4)
(2, 5)
(3, 6)



for i in zip(*zip([1,2,3],[4,5,6])):
    print(i)

(1, 2, 3)
(4, 5, 6)

3带*的表达式可以获取序列的一部分

*a,b,c = 1,2,3,4,5
a
Out[8]: [1, 2, 3]
b
Out[9]: 4
c
Out[10]: 5
#同样的
a,*b,c=1,2,3,4,5
a
Out[12]: 1
b
Out[13]: [2, 3, 4]
c
Out[14]: 5