Going through Python 3's ChainMap

python-chain-map.py

from collections import ChainMap

# Traditionally, you can combine dictionaries into one,
# however, this creates a totally new dictionary

# e.g. for Python 3.5, you could do this:

a = {'name': 'Andela'}
b = {'class': 'World'}

c = {**a, **b}

# Notice, if a or b are updated, (obviously) c does not change
# And c, will be using extra memory the size of a + b

# With ChainMap
d = ChainMap(a, b)  

print d # ChainMap({'name': 'Andela'}, {'class': 'World'})

print d['name'] # 'Andela'

# However, note that ChainMap only creates an interface through which
# the specific values of the dictionaries can be accessed.

# There's a catch though. If we have duplicate keys with different values,
# Only the first one will be picked, e.g.

d = ChainMap(a, b, {'name': 'NG'})
print d # 'Andela'

d = ChainMap({'name': 'NG'}, a, b}
print d # 'NG'

# Conclusion: the beauty of ChainMap is in the ability to create
# a handy interface through which you can access multiple dictionaries
# at once; with minimal extra memory usage.