python 解包

解包sequence

>>> p = (4, 5)
>>> x, y = p
>>> x
4
>>> y
5
>>>
>>> data = [ 'ACME', 50, 91.1, (2012, 12, 21) ]
>>> name, shares, price, date = data
>>> name
'ACME'
>>> date
(2012, 12, 21)
>>> name, shares, price, (year, mon, day) = data
>>> name
'ACME'
>>> year
2012
>>> mon
12
>>> day
21
>>>

解包string

>>> s = 'Hello'
>>> a, b, c, d, e = s
>>> a
'H'
>>> b
'e'
>>> e
'o'
>>>

解包指定定內容

>>> data = [ 'ACME', 50, 91.1, (2012, 12, 21) ]
>>> _, shares, price, _ = data
>>> shares
50
>>> price
91.1

前後任意長度解包

中間

def drop_first_last(grades):
    first, *middle, last = grades
    return avg(middle)

最後

>>> record = ('Dave', '[email protected]', '773-555-1212', '847-555-1212')
>>> name, email, *phone_numbers = user_record
>>> name
'Dave'
>>> email
'[email protected]'
>>> phone_numbers
['773-555-1212', '847-555-1212']

第一個

>>> *trailing, current = [10, 8, 7, 1, 9, 5, 10, 3]
>>> trailing
[10, 8, 7, 1, 9, 5, 10]
>>> current
3

解包包含tag的元組

records = [
('foo', 1, 2),
('bar', 'hello'),
('foo', 3, 4),
]
def do_foo(x, y):
    print('foo', x, y)
def do_bar(s):
    print('bar', s)
for tag, *args in records:
    if tag == 'foo':
        do_foo(*args)
    elif tag == 'bar':
        do_bar(*args)

解包實際應用

>>> line = 'nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false'
>>> uname, *fields, homedir, sh = line.split(':')
>>> uname
'nobody'
>>> homedir
'/var/empty'
>>> sh
'/usr/bin/false'

數組裏面有元組的情況

>>> record = ('ACME', 50, 123.45, (12, 18, 2012))
>>> name, *_, (*_, year) = record
>>> name
'ACME'
>>> year
2012

分割遞歸方法

>>> def sum(items):
        head, *tail = items
        return head + sum(tail) if tail else head
>>> sum(items)
36
>>>