Python Data Structure 简明教程
Python - Maps
Python Maps 又称为 ChainMap，是一种数据结构，可同时管理多个字典为一个单位。组合的字典包含特定序列中的键和值对，消除了任何重复的键。ChainMap 的最佳用途是同时搜索多个字典并获得适当的键值对映射。我们还看到这些 ChainMaps 的行为类似堆栈数据结构。
Python Maps also called ChainMap is a type of data structure to manage multiple dictionaries together as one unit. The combined dictionary contains the key and value pairs in a specific sequence eliminating any duplicate keys. The best use of ChainMap is to search through multiple dictionaries at a time and get the proper key-value pair mapping. We also see that these ChainMaps behave as stack data structure.
Creating a ChainMap
我们创建两个字典，并使用 collections 库中的 ChainMap 方法对它们进行组合。然后，我们打印字典组合结果的键和值。如果存在重复键，则仅保留第一个键的值。
We create two dictionaries and club them using the ChainMap method from the collections library. Then we print the keys and values of the result of the combination of the dictionaries. If there are duplicate keys, then only the value from the first key is preserved.
Example
import collections
dict1 = {'day1': 'Mon', 'day2': 'Tue'}
dict2 = {'day3': 'Wed', 'day1': 'Thu'}
res = collections.ChainMap(dict1, dict2)
# Creating a single dictionary
print(res.maps,'\n')
print('Keys = {}'.format(list(res.keys())))
print('Values = {}'.format(list(res.values())))
print()
# Print all the elements from the result
print('elements:')
for key, val in res.items():
print('{} = {}'.format(key, val))
print()
# Find a specific value in the result
print('day3 in res: {}'.format(('day1' in res)))
print('day4 in res: {}'.format(('day4' in res)))Output
执行上述代码后，将生成以下结果 −
When the above code is executed, it produces the following result −
[{'day1': 'Mon', 'day2': 'Tue'}, {'day1': 'Thu', 'day3': 'Wed'}]
Keys = ['day1', 'day3', 'day2']
Values = ['Mon', 'Wed', 'Tue']
elements:
day1 = Mon
day3 = Wed
day2 = Tue
day3 in res: True
day4 in res: FalseMap Reordering
如果在上例中组合字典时更改字典的顺序，我们会看到元素的位置会像在连续链中一样交换。这再次显示了映射作为堆栈的行为。
If we change the order the dictionaries while clubbing them in the above example we see that the position of the elements get interchanged as if they are in a continuous chain. This again shows the behavior of Maps as stacks.
Updating Map
当更新字典的元素时，将在 ChainMap 的结果中立即更新结果。在下面的示例中，我们看到新的更新值反映在结果中，而无需显式再次应用 ChainMap 方法。
When the element of the dictionary is updated, the result is instantly updated in the result of the ChainMap. In the below example we see that the new updated value reflects in the result without explicitly applying the ChainMap method again.