ChainMap简单示例

ChainMap是dict的子类,拥有dict的所有功能, 感觉用它的地方吧???

 

from collections import ChainMap

"""
     相当于join两个dict的操作

"""

# 示例1
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}

chain_dict = ChainMap(dict1, dict2)
for k, v in chain_dict.items():
    print(k, v)

'''
打印结果:
c 3
d 4
a 1
b 2
'''

print('-' * 50)

# 示例2

dict1 = {"a": 1, "b": 2}
dict2 = {"b": 3, "d": 4}

chain_dict = ChainMap(dict1, dict2)
for k, v in chain_dict.items():
    print(k, v)

'''
打印结果: b只出现了一次,就是首次的值
b 2
d 4
a 1

'''
print('-' * 50)
# 示例3
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}

chain_dict = ChainMap(dict1, dict2)

chain_dict.update({'e': 8})


for k,v in chain_dict.items():
    print(k,v)

'''
c 3
d 4
a 1
b 2
e 8
'''

print('-' * 50)
# 示例4
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}

chain_dict = ChainMap(dict1, dict2)

print(chain_dict)

# Remove and return an item pair from maps[0]. Raise KeyError is maps[0] is empty.'  感觉没啥用
item = chain_dict.popitem()
print(item)  # ('b', 2)

# pop也只能弹出chain_map[0]中的元素,有点鸡
value = chain_dict.pop('a')
print(value)  #1
print(chain_dict)    # ChainMap({}, {'c': 3, 'd': 4})


print('-' * 50)
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}

chain_dict = ChainMap(dict1, dict2)

# new_chain_dict = chain_dict.new_child()
# print(new_chain_dict)  # ChainMap({}, {'a': 1, 'b': 2}, {'c': 3, 'd': 4})  , 这有啥用呀

# 在chain_map添加一个新的dict 
new_chain_dict = chain_dict.new_child({'name':'admin'})
print(new_chain_dict)  # ChainMap({'name': 'admin'}, {'a': 1, 'b': 2}, {'c': 3, 'd': 4})