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python学习笔记: collections模块

python学习笔记: collections模块

作者: lafrinte | 来源:发表于2017-11-11 22:41 被阅读0次

    1. collections模块介绍

    collections模块在原生python数据类型的基础上提供了新的数据类型:

    • namedtuple: 生成可以使用名字来访问元素内容的tuple子类
    • deque: 双端队列,可以快速的从另外一侧追加和推出对象
    • Counter: 计数器,主要用来计数
    • OrderedDict: 有序字典
    • defaultdict: 带有默认值的字典

    2. 使用介绍

    2.1 namedtuple

    namedtuple主要用来产生可以使用名称来访问元素的数据对象,通常用来增强代码的可读性,例如:

    In [1]: from collections import namedtuple
    
    In [2]: websites = [
       ...:     ('google', 'http://www.google.com/', 'search engine'),
       ...:     ('Sina', 'http://www.sina.com.cn/', 'blog'),
       ...:     ('taobao', 'http://www.taobao.com/', 'shopping store')
       ...: ]
    
    In [3]: Website = namedtuple('Website', ['name', 'url', 'remark'])
    
    In [4]: for website in websites:
       ...:     website = Website._make(website)
       ...:     print website
       ...:
    Website(name='google', url='http://www.google.com/', remark='search engine')
    Website(name='Sina', url='http://www.sina.com.cn/', remark='blog')
    Website(name='taobao', url='http://www.taobao.com/', remark='shopping store')
    
    In [5]: p = Website('w3', 'www.w3school.com.cn', 'study')
    
    In [6]: p
    Out[6]: Website(name='w3', url='www.w3school.com.cn', remark='study')
    
    In [7]: d = p._asdict()
    
    In [8]: d['name']
    Out[8]: 'w3'
    
    In [9]: d['url']
    Out[9]: 'www.w3school.com.cn'
    

    2.2 deque

    deque是双端队列,可以从队列的头部增加或取出对象,相较于list,在数据量大的情况下能提高运行速度。

    In [1]: from collections import deque
    
    In [2]: p = deque([1, 2, 3, 4])
    
    In [3]: p.append(5)
    
    In [4]: p.appendleft(0)
    
    In [5]: p
    Out[5]: deque([0, 1, 2, 3, 4, 5])
    

    2.3 defaultdict

    defaultdict可传入一个工厂函数,在请求字典内不存在的key时,将调用工厂函数方法,将结果作为key的默认值,避免标准字典类型的KeyError错误。

    In [1]: from collections import
    
    In [2]: d = defaultdict(lambda: 'None')
    
    In [3]: d[1]
    Out[4]: 'None'
    
    In [5]: members = [
        ...:     ['male', 'John'],
        ...:     ['male', 'Jack'],
        ...:     ['female', 'Lily'],
        ...:     ['male', 'Pony'],
        ...:     ['female', 'Lucy'],
        ...: ]
    
    In [6]: result = defaultdict(list)
    
    In [7]: for sex, name in members:
        ...:     result[sex].append(name)
        ...:
    
    In [8]: print result
    defaultdict(<type 'list'>, {'male': ['John', 'Jack', 'Pony'], 'female': ['Lily', 'Lucy']})
    

    2.4 OrderedDict

    OrderedDict不同于Dict, 它是一个有序的字典对象。

    In [1]: from collections import OrderedDict
    
    In [2]: items = (
       ...:     ('A', 1),
       ...:     ('B', 2),
       ...:     ('C', 3),
       ...:     ('D', 4)
       ...: )
    
    In [3]: regular_dict = dict(items)
    
    In [4]: ordered_dict = OrderedDict(items)
    
    In [5]: for k, v in regular_dict.iteritems():
       ...:     print "regular dict %s = %s" % (k, v)
       ...:
    regular dict A = 1
    regular dict C = 3
    regular dict B = 2
    regular dict D = 4
    
    In [6]: for k, v in ordered_dict.iteritems():
       ...:     print "ordered dict %s = %s" % (k, v)
       ...:
    ordered dict A = 1
    ordered dict B = 2
    ordered dict C = 3
    ordered dict D = 4
    

    2.5 Counter

    Counter是一个计数器,可以用来统计字符出现次数

    In [1]: from collections import Counter
    
    In [2]: c = Counter()
    
    In [3]: for s in '111345eeabab':
       ...:     c[s] = c[s] + 1
       ...:
    
    In [4]: c
    Out[4]: Counter({'1': 3, '3': 1, '4': 1, '5': 1, 'a': 2, 'b': 2, 'e': 2})
    

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