Python交换字典键值对的四种方法实例

data= {'A':1, 'B':2, 'C':3}
new_data = dict(zip(data.values(), data.keys()))
print(new_data)
# 运行结果
# {1: 'A', 2: 'B', 3: 'C'}

data= {'A':1, 'B':2, 'C':3}
new_data = {}
for key, val in data.items():
    new_data[val] = key
print(new_data)
# 运行结果
# {1: 'A', 2: 'B', 3: 'C'}

new_data = dict([val, key] for key, val in data.items())
print(new_data)
# 运行结果
# {1: 'A', 2: 'B', 3: 'C'}

from collections import defaultdict

def main():
    data = {'A': 1, 'B': 2, 'C': 3, 'D': 3}
    new_data = defaultdict(list)
    for key, val in data.items():
        new_data[val].append(key)
    print(new_data)
# 运行结果
# {1: ['A'], 2: ['B'], 3: ['C', 'D']}

dict = defaultdict(factory_function)
# factory_function可以是list、set、str等等，作用是当key不存在时，返回的是工厂函数的默认值