python cookbook 第一章阅读笔记

Python进阶技巧

最新推荐文章于 2023-12-16 14:30:07 发布

原创最新推荐文章于 2023-12-16 14:30:07 发布 · 313 阅读

0 ·

CC 4.0 BY-SA版权

python 专栏收录该内容

1 篇文章

订阅专栏

本文介绍了Python编程中的高级技巧，包括使用星号(*)操作符来分解序列、利用deque实现固定长度的队列、寻找序列中的最大或最小元素、利用defaultdict进行多重映射以及通过OrderedDict保持字典项的插入顺序等。

1.2 从人意长度的可迭代对象中分解元素：

def drop_first_last(grades):

    first,*middle,last = grades

    return avg(middle)

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

总结：＊的语法在迭代一个边长的元组序列时尤为重要

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

1.3 保存最后n个元素

from collections import deque
q = deque(maxlen=3)
q.append(1)
q.append(2)
q.append(3)
q.append(4)
q
deque([2,3,4],maxlen=3)

1.4 找到最大或者最小的n个元素

a = [1,2,3,4,5,6]
import heapq
print(heapq.nlargest(3,a)
print(heapq.nsmallest(3,a)
def find_largest(a_list,num):
    a_list.sort()
    return a_list[-num:]

1.6 在字典中将建映射到多个值上

>>> from collections import defaultdict
>>> d = defaultdict(list)
>>> d['a'].append(1)
>>> d['a'].append(2)
>>> d['b'].append(3)
>>> d
defaultdict(<type 'list'>, {'a': [1, 2], 'b': [3]})

1.7让字典保持有序

OrderedDict维护双向链表，根据元素加入的顺序排列键的位置。大小是普通字典的2倍

>>> from collections import OrderedDict
>>> d = OrderedDict()
>>> d['foo'] = 1
>>> d['bar'] = 2
>>> d
OrderedDict([('foo', 1), ('bar', 2)])

1.8 与字典有关的计算

>>> prices = { 'ibm':30,
...            'apple':50,
...            'cisco':30,
...            'facebook':100}
>>> min_price = min(zip(prices.values(),prices,keys()))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'keys' is not defined
>>> min_price = min(zip(prices.values(),prices.keys()))
>>> min_price
(30, 'cisco')
>>> price_sorted = sorted(zip(prices.values(),prices.keys()))
>>> price_sorted
[(30, 'cisco'), (30, 'ibm'), (50, 'apple'), (100, 'facebook')]
>>> price_test = sorted(prices)
>>> price_test
['apple', 'cisco', 'facebook', 'ibm']