【问题】
将lst = [ [1, 2, 3], [2, 1, 3], [8, 4, 3] ]，变为[1, 2, 3, 2, 1, 3, 8, 4, 3]
【方法】
1. myList = [x for j in lst for x in j]
2.
mylist = []
for i in L:
mylist += i
print(mylist)
3. 使用标准库中的itertools（循环器）
from itertools import chain
mylist = list(chain(*lst))
print(mylist)
