Python 字典默认值设置_python字典默认值

# -*- coding: utf-8 -*-
"""
Created on Tue May 17 15:19:30 2022
@author: 12506
"""
 
#还有dic.get()方法，看参考
 
 
# =============================================================================
# # 这种是会报错的，因为字典中没有key的记录
# strings = ('puppy', 'kitten', 'puppy', 'puppy',
#            'weasel', 'puppy', 'kitten', 'puppy')
# counts = {}
#
# for kw in strings:
#     counts[kw] += 1
# =============================================================================
 
# 改进1：思想：第一次统计时候设置默认值1
# =============================================================================
# strings = ('puppy', 'kitten', 'puppy', 'puppy',
#            'weasel', 'puppy', 'kitten', 'puppy')
# counts = {}
#
# for kw in strings:
#     if kw not in counts:
#         counts[kw] = 1
#     else:
#         counts[kw] += 1
#
# # counts:
# # {'puppy': 5, 'weasel': 1, 'kitten': 2}
#
# =============================================================================
 
# 改进2：使用setdefault()函数:第一个参数是key的名称,第二个参数是默认值
# =============================================================================
# strings = ('puppy', 'kitten', 'puppy', 'puppy',
#            'weasel', 'puppy', 'kitten', 'puppy')
# counts = {}
#
# for kw in strings:
#     counts[kw] = counts.setdefault(kw, 0) + 1
# =============================================================================
 
 
# 以上方法已可以解决  字典默认值问题
# 下面给出一种字典本身提供的默认值功能：collections.defaultdict(factory_function)
# factory_function可以是list、set、str、int：当key不存在时候，返回默认值
 
# =============================================================================
# from collections import defaultdict
#
# dict1 = defaultdict(int)
# dict2 = defaultdict(set)
# dict3 = defaultdict(str)
# dict4 = defaultdict(list)
# dict1[2] = 'two'
#
# print(dict1[1])
# print(dict2[1])
# print(dict3[1])
# print(dict4[1])
#
# # output:
# # 0
# # set()
# #
# # []
# # dict1: defaultdict(int, {2: 'two', 1: 0})
# =============================================================================
# =============================================================================
# from collections import defaultdict
# # collections 类似一个类，用来初始化一个指定类型的字典
# dic = defaultdict(list)
# # dic: defaultdict(list, {})
# dic['a']
# # dic: defaultdict(list, {'a': []})
# dic['b'].append('qq')
# # dic: defaultdict(list, {'a': [], 'b': ['qq']})
# dic.get('ss')  # dict.get返回指定键的值，如果值不在字典中返回default值
# dic['ss']
# # dic: defaultdict(list, {'a': [], 'b': ['qq'], 'ss': []})
# =============================================================================
 
# =============================================================================
# # 上面的单词统计
# from collections import defaultdict
#
# strings = ('puppy', 'kitten', 'puppy', 'puppy',
#            'weasel', 'puppy', 'kitten', 'puppy')
# counts = defaultdict(lambda: 0)  # 使用lambda来定义简单的函数
#
# for s in strings:
#     counts[s] += 1
# # counts: defaultdict(<function __main__.<lambda>()>, {'puppy': 5, 'kitten': 2, 'weasel': 1})
# =============================================================================

参考

参考2dic.get