解包，个人理解就是对序列进行拆分，赋值给对应的变量
最经典的莫过于两个数交换，一般我们是通过一个中间变量把两个数交换，在python中可以直接通过解包的形式直接交换两个数
如：
In [92]: a,b=1,3
In [93]: a
Out[93]: 1
In [94]: b
Out[94]: 3
In [96]: a,b=3,1
In [97]: a
Out[97]: 3
In [98]: b
Out[98]: 1
In [99]:
其实 a, b = 1, 3 就是 a, b = (1, 3), 把序列中对应的元素赋值给a，b
再看一组例子
In [99]: head, *tail = [1,2,3,4,5]
In [100]: head
Out[100]: 1
In [101]: tail
Out[101]: [2, 3, 4, 5]
In [104]: head, *_, tail = [1,2,3,4,5]
In [105]: head
Out[105]: 1
In [106]: tail
Out[106]: 5
In [107]: _
Out[107]: 5
In [108]: head, *mid, tail = [1,2,3,4,5]
In [109]: mid
Out[109]: [2, 3, 4]
In [120]: head, _, *mid, tail = [1,2,3,4,5]
In [121]: head
Out[121]: 1
In [122]: mid
Out[122]: [3, 4]
In [123]: tail
Out[123]: 5
In [115]: h, *t = ['a']
In [116]: h
Out[116]: 'a'
In [117]: t
Out[117]: []
In [124]: a, (b, c), d = [1, [2,3],4]
In [125]: a
Out[125]: 1
In [126]: b
Out[126]: 2
In [127]: c
Out[127]: 3
In [128]: d
Out[128]: 4
从上面可以感受到解包的强大之处，如果元素个数有多个，想解包后放在一个变量里面就要使用*变量名，_用作变量名时表示丢弃这些变量，python中单个_表示上一个命令的返回值，*变量名解包后都是一个列表
封包
封包就是把多个元素打包赋值给一个变量，函数中返回多个值就是一个封包
In [118]: v = 1,2,3
In [119]: v
Out[119]: (1, 2, 3)
