ChainMap

A ChainMap encapsulates many dictionaries into a single unit and returns a list of dictionaries.

# 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)

ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6})

Accessing Keys and Values from ChainMap Values from ChainMap can be accessed using the key name. They can also be accessed by using the keys() and values() method.

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)

# Accessing Values using key name
print(c['a'])

# Accessing values using values()
# method
print(c.values())

# Accessing keys using keys()
# method
print(c.keys())

1
ValuesView(ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6}))
KeysView(ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4}, {'e': 5, 'f': 6}))

Adding new dictionary

A new dictionary can be added by using the new_child() method. The newly added dictionary is added at the beginning of the ChainMap.

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
print ("All the ChainMap contents are : ")
print (chain)

# using new_child() to add new dictionary
chain1 = chain.new_child(dic3)

# printing chainMap
print ("Displaying new ChainMap : ")
print (chain1)

All the ChainMap contents are : 
ChainMap({'a': 1, 'b': 2}, {'b': 3, 'c': 4})
Displaying new ChainMap : 
ChainMap({'f': 5}, {'a': 1, 'b': 2}, {'b': 3, 'c': 4})