collectons模块

Counter计数

a=[1,2,3,2,4,4,3,5,3,5,4,6,4,5,3,5,35,2,3,5,3] 
from collections import Counter
Counter(a)                      统计次数
Counter(a)[3]                   某个值出现的次数
Counter(a).elements(2)          输出频率最高的两个
update()                        相加
subtract()                      相减
                 

 

 

ChainMap映射多个字典

a = {'x': 1, 'z': 3 }
b = {'y': 2, 'z': 4 ,'a':55}
from collections import ChainMap
f = ChainMap(a,b)
f['x'] # 1
f['y'] # 2 a中没找到，在b中找
f['z'] # 3 找到就不找了
f['y'] = 'yyy' # a新增一个键值对，{'x': 1, 'z': 3, 'y': 'yyy'}
f['d'] = 'rrr' # a新增一个键值对，{'x': 1, 'z': 3, 'd': 'ddd', 'y': 'yyy'}

 

 

UserDict重写字典

form collections import UserDict
class StrKeyDict(UserDict):
    def __missing__(self, key):
        if isinstance(key, str):
            raise KeyError(key)
        return self[str(key)]  # 调用__getitem__方法
    def __contains__(self, key):
        print('contions')
        return str(key) in self.data
    def __setitem__(self, key, item):
        """当key不存在时，调用__missing__方法"""
        self.data['f1'] = 'ttt'
        print(self.data)
        print("key:",key)
        print("item:",item)
        if key not in self.data:
            self.data[str(key)] = item
f=StrKeyDict()
f['x'] = 123
print(f)
返回:
{'f1': 'ttt'}
key: x
item: 123
{'x': 123, 'f1': 'ttt'}

 

 

namedtuple 命名元组

namedtuple是一个函数，用来创建一个自定义的tuple对象，规定了tuple元素的个数，可以用属性来引用tuple的某个元素。

>>> from collections import namedtuple
>>> Point = namedtuple('Point', ['x', 'y'])
>>> p = Point(11, 22)
>>> p.x
11
>>> p.y
22