ChainMap用法

from collections import ChainMap

这是ChainMap的parents和new_child()用法

values = ChainMap()
values[‘x’] = 3
values = values.new_child()
values[‘x’] = 2
print(values)
values = values.new_child()
print(values)
values[‘x’] = 1
print(values)
print(values[‘x’])
values = values.parents
print(values[‘x’])

output

ChainMap({‘x’: 2}, {‘x’: 3})
ChainMap({}, {‘x’: 2}, {‘x’: 3})
ChainMap({‘x’: 1}, {‘x’: 2}, {‘x’: 3})
1
2

基本用法

from collections import ChainMap
dict1 = {‘a’:1,’b’:2}
dict2 = {‘a’:9,’c’:3}
chain_dict = ChainMap(dict1,dict2) #Chainmap会根据dict1和dict2的变化而变化，优先在dict1中查找
print(chain_dict[‘a’])
dict1.update(dict2) #update不会根据dict2的变化而变化，结果根据dict2的值而定
dict2[‘c’] = 6
print(dict1)
print(chain_dict)

output

1
{‘a’: 9, ‘b’: 2, ‘c’: 3}
ChainMap({‘a’: 9, ‘b’: 2, ‘c’: 3}, {‘a’: 9, ‘c’: 6})