ChainMap in Python
Python contains a container called “ChainMap” which encapsulates many dictionaries into one unit. ChainMap is member of module “collections“.
Example:
# Python program to demonstrate the use of # 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) |
Output:
ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6})
Let’s review various Operations enabled ChainMap
Access Operations
- keys() :-This function/method is have used to display all the keys of all the dictionaries in ChainMap.
- values() :- This function/method is have used to display values of all the dictionaries in ChainMap.
- maps() :- This function/method is have used to display keys with corresponding values of all the dictionaries in ChainMap.
# Please select Python 3 for running this code in IDE# Python code to demonstrate ChainMap and # keys(), values() and maps# importing collections for ChainMap operationsimportcollections# initializing dictionariesdic1={'a':1,'b':2}dic2={'b':3,'c':4}# initializing ChainMapchain=collections.ChainMap(dic1, dic2)# printing chainMap using mapsprint("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()))
Output :
- 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]
- Note : Notice the key named “b” exists in both dictionaries, but just first dictionary key is taken when key value of “b”. Ordering is done when the dictionaries are passed in function.
Manipulating Operations
- new_child() :-This function/method adds a new dictionary in the beginning of the ChainMap.
- reversed() :- This function/method reverses the relative ordering of dictionaries in the ChainMap.
# 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']) |
Output :
- 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