ChainMap

# 链map
from collections import ChainMap

a = {'x': 1, 'z': 3}
b = {'y': 2, 'z': 4}

c = ChainMap(a, b)
print(c['x'])
print(c['y'])
print(c['z'])  # 3 重复的会使用第一个，修改删除都是只针对第一个

print(len(c))  # 3
print(list(c.keys()))  # ['y', 'z', 'x']
print(list(c.values()))  # [2, 3, 1]

c['z'] = 10
c['w'] = 40
del c['x']
print(a)  # {'z': 10, 'w': 40}
print(c)  # ChainMap({'z': 10, 'w': 40}, {'y': 2, 'z': 4})
# del c['y'] # KeyError: "Key not found in the first mapping: 'y'"


values = ChainMap()
values['x'] = 1
values = values.new_child()
values['x'] = 2
values = values.new_child()
values['x'] = 3

print(values)  # ChainMap({'x': 3}, {'x': 2}, {'x': 1})
print(values.parents)  # ChainMap({'x': 2}, {'x': 1})
print(values.parents.parents)  # ChainMap({'x': 1})