2016.07.09-10 packing/unpicking

packing/unpicking(封包\解包)
    解包(unpicking)把可迭代队形的元素赋值给变量
    封包（picking）是把变量构建成元组
    x, y =(1, 3)
    x, y =[1, 3]

    #*mid 表示一个容器，可以包含任意多个元素，解包过程中只能有一个*，*赋值出来的都是列表
    >>> head, *tail = list(range(10))
    >>> head
    0
    >>> tail
    [1, 2, 3, 4, 5, 6, 7, 8, 9]

    >>> head, *mid ,tail = list(range(10))
    >>> head
    0
    >>> mid
    [1, 2, 3, 4, 5, 6, 7, 8]
    >>> tail
    9
    >>> 

    #取头和尾，_表示将变量丢弃
    >>> h, *_, t = list(range(10))
    >>> h
    0
    >>> t
    9
    >>> 

    >>> a, (b, c), d = [1 ,[2, 3], 4]
    >>>
    >>> a
    1
    >>> b
    2
    >>> c
    3
    >>> d
    4
    >>> 

    >>> a, (b, *_, c), d = [1, [2, 3, (4, 5, 6), 7, 8, 9], 10]
    >>> a
    1
    >>> b
    2
    >>> c
    9
    >>> d
    10
    >>>