Python中的字典一键多值的四种写法小结

my_dict = {}

# 添加值
my_dict.setdefault('key1', []).append('value1')
my_dict.setdefault('key1', []).append('value2')

# 结果
print(my_dict)  # 输出: {'key1': ['value1', 'value2']}

my_dict = {}

# 添加值
my_dict.setdefault('key1', set()).add('value1')
my_dict.setdefault('key1', set()).add('value2')
my_dict.setdefault('key1', set()).add('value1')  # 重复值不会被添加

# 结果
print(my_dict)  # 输出: {'key1': {'value1', 'value2'}}

from collections import defaultdict

# 使用列表
my_dict = defaultdict(list)
my_dict['key1'].append('value1')
my_dict['key1'].append('value2')

print(my_dict)  # 输出: defaultdict(<class 'list'>, {'key1': ['value1', 'value2']})

# 使用集合
my_dict = defaultdict(set)
my_dict['key1'].add('value1')
my_dict['key1'].add('value2')
my_dict['key1'].add('value1')  # 重复值不会被添加

print(my_dict)  # 输出: defaultdict(<class 'set'>, {'key1': {'value1', 'value2'}})

my_dict = {}

# 添加值
if 'key1' not in my_dict:
    my_dict['key1'] = []
my_dict['key1'].append('value1')
my_dict['key1'].append('value2')

print(my_dict)  # 输出: {'key1': ['value1', 'value2']}

key = 0
value = [1,5]
exp = dict()
exp.setdefault(key,[]).append(value) 
value = [2,5]
exp.setdefault(key,[]).append(value)
print(exp)

key = 0
value = 1
exp = dict()
exp.setdefault(key,set()).add(value) 
value = 2
exp.setdefault(key,set()).add(value)
print(exp)

import collections
 
key = 0
value = 1
exp = collections.defaultdict(list)
exp[key].append(value)
value = 1
exp[key].append(value)
print(exp)

import collections
 
key = 0
value = 1
exp = collections.defaultdict(set)
exp[key].add(value)
value = 1
exp[key].add(value)
value = 5
exp[key].add(value)
print(exp)