这周我们学习了
==和is
is 是比较两个引用是否指向了同一个对象（引用比较）
== 是比较两个对象是否相等
列表推导式
a = [x for x in range(4)]
a = [0,1,2,3]
a = [x for x in range(3,4)]
a = [3]
3个for循环
a = [x,y,z]for x in range(1,3) for y in range(3) for z in range(4,6)]
a
[(1,0,4),
(1,0,5),
(1,1,4),
(1,1,5),
(1,2,4),
(1,2,5),
(2,0,4),
(2,0,5),
(2,1,4),
(2,1,5),
(2,2,4),
(2,2,5)]
