一文带你深入探究Python Collections模块

import collections
​
mp = collections.defaultdict(list)
​
words = ['apple', 'banana', 'orange', 'pear', 'peach']
for word in words:
    mp[word[0]].append(word)
​
print(mp) # defaultdict(<class 'list'>, {'a': ['apple'], 'b': ['banana'], 'o': ['orange'], 'p': ['pear', 'peach']})

import collections
​
s = "abracadabra"
counter = collections.Counter(s)
print(counter) # 输出结果：Counter({'a': 5, 'b': 2, 'r': 2, 'c': 1, 'd': 1})

import collections
​
Point = collections.namedtuple('Point', ['x', 'y'])
p = Point(11, y=22)
print(p.x, p.y) # 输出结果：11 22

import collections
​
q = collections.deque(maxlen=3)
q.append(1)
q.append(2)
q.append(3)
print(q)  # 输出结果：deque([1, 2, 3], maxlen=3)
q.append(4)
print(q)  # 输出结果：deque([2, 3, 4], maxlen=3)

from collections import OrderedDict
​
class LRUCache:
    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = OrderedDict()
​
    def get(self, key):
        if key in self.cache:
            value = self.cache[key]
            # 将访问的元素移到字典的末尾
            self.cache.move_to_end(key)
            return value
        else:
            return -1
​
    def put(self, key, value):
        if key in self.cache:
            # 如果key已经存在，将其移到字典的末尾
            self.cache.move_to_end(key)
        self.cache[key] = value
        if len(self.cache) > self.capacity:
            # 如果缓存已满，淘汰最早访问的元素
            self.cache.popitem(last=False)

from collections import ChainMap
​
dict1 = {'a': 1, 'b': 2}
dict2 = {'c': 3, 'd': 4}
dict3 = {'e': 5, 'f': 6}
​
chain_map = ChainMap(dict1, dict2, dict3)
​
value = chain_map['a']
print(value)  # 输出: 1
​
value = chain_map['c']
print(value)  # 输出: 3

from collections import UserDict
​
class MyDict(UserDict):
    def __setitem__(self, key, value):
        super().__setitem__(key, value * 2)
​
my_dict = MyDict()
my_dict['a'] = 1
my_dict['b'] = 2
​
print(my_dict)  # 输出: {'a': 2, 'b': 4}

from collections import UserList
​
class MyList(UserList):
    def remove_duplicates(self):
        self.data = list(set(self.data))
​
my_list = MyList([1, 2, 2, 3, 4, 4, 5])
my_list.remove_duplicates()
​
print(my_list)  # 输出: [1, 2, 3, 4, 5]

from collections import UserString
​
class MyString(UserString):
    def remove_whitespace(self):
        self.data = self.data.replace(' ', '')
​
my_string = MyString('Hello World')
my_string.remove_whitespace()
​
print(my_string)  # 输出: HelloWorld