Python 中的链图
Python 包含一个名为“ ChainMap ”的容器，它将许多词典封装成一个单元。ChainMap 是模块“ ”集合“ ”的成员。
示例:
# Python program to demonstrate
# ChainMap
from collections import ChainMap
d1 = {'a': 1, 'b': 2}
d2 = {'c': 3, 'd': 4}
d3 = {'e': 5, 'f': 6}
# Defining the chainmap
c = ChainMap(d1, d2, d3)
print(c)
输出:
ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6})
我们来看看链图上的各种操作
访问操作
-
keys() :- This function is used to display all the keys of all the dictionaries in ChainMap. values() :- This function is used to display *values of all the dictionaries in ChainMap.* *maps() :- This function is used to display *keys with corresponding values of all the dictionaries in ChainMap.
```py
Please select Python 3 for running this code in IDE
Python code to demonstrate ChainMap and
keys(), values() and maps
importing collections for ChainMap operations
import collections
initializing dictionaries
dic1 = { 'a' : 1, 'b' : 2 } dic2 = { 'b' : 3, 'c' : 4 }
initializing ChainMap
chain = collections.ChainMap(dic1, dic2)
printing chainMap using maps
print ("All the ChainMap contents are : ") print (chain.maps)
printing keys using keys()
print ("All keys of ChainMap are : ") print (list(chain.keys()))
printing keys using keys()
print ("All values of ChainMap are : ") print (list(chain.values())) ```
输出:
```py All the ChainMap contents are : [{'b': 2, 'a': 1}, {'c': 4, 'b': 3}] All keys of ChainMap are : ['a', 'c', 'b'] All values of ChainMap are : [1, 4, 2]
```
注意:注意两个字典中都存在名为“b”的关键字，但只有第一个字典关键字作为“b”的键值。当字典按功能传递时，排序就完成了。
操作操作** * *new_child() :- This function adds a new dictionary in the beginning of the ChainMap.* ***reversed() :- This function reverses the relative ordering of dictionaries in the ChainMap.
```py
Please select Python 3 for running this code in IDE
Python code to demonstrate ChainMap and
reversed() and new_child()
importing collections for ChainMap operations
import collections
initializing dictionaries
dic1 = { 'a' : 1, 'b' : 2 } dic2 = { 'b' : 3, 'c' : 4 } dic3 = { 'f' : 5 }
initializing ChainMap
chain = collections.ChainMap(dic1, dic2)
printing chainMap using map
print ("All the ChainMap contents are : ") print (chain.maps)
using new_child() to add new dictionary
chain1 = chain.new_child(dic3)
printing chainMap using map
print ("Displaying new ChainMap : ") print (chain1.maps)
displaying value associated with b before reversing
print ("Value associated with b before reversing is : ",end="") print (chain1['b'])
reversing the ChainMap
chain1.maps = reversed(chain1.maps)
displaying value associated with b after reversing
print ("Value associated with b after reversing is : ",end="") print (chain1['b']) ```
输出:
```py All the ChainMap contents are : [{'b': 2, 'a': 1}, {'b': 3, 'c': 4}] Displaying new ChainMap : [{'f': 5}, {'b': 2, 'a': 1}, {'b': 3, 'c': 4}] Value associated with b before reversing is : 2 Value associated with b after reversing is : 3
```
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