defaultdict使用及__missing__理解

import collections
import re

WORD_RE = re.compile(r'\w+')

index = collections.defaultdict(list) #用list方法作为默认工厂创建一个默认字典
with open('xx.txt',encoding='utf-8') as fp:
    for line_no,line in enumerate(fp,1):
        for match in WORD_RE.findeiter(line):
            word = match.group()
            column_no = match.start()+1
            location = (line_no,column_no)
            index[word].append(location) # 如果index没有Word记录，会调用默认工厂，创建一个空列表

for word in sorted(index,key=str.upper):
    print(word,index[word])

 

import collections

class StrKeyDict(collections.UserDict):
    def __missing__(self,key):
        if isinstance(key,str):
            raise KeyError(key)
        return self[str(key)]
    def __contains__(self,key):
        return str(key) in self.data

    def __setitem__(self,key,item):
        self.data[str(key)] = item

 不可变映射类型

import collections
from types import MappingProxyType

d = {1:'A'}
d_proxy = MappingProxyType(d)
d_proxy[1] # A
d_proxy[2] #报错因为不可变
d_proxy[2] = 'B' #{1:'A',2:'B'}