DefaultDict

from collections import defaultdict

##### USING INDUILT FUNCTION #####
default_dict1 = defaultdict(int, {'a':10, 'b':20})

print(default_dict1['a'])    # 10
print(default_dict1['b'])    # 20
print(default_dict1['c'])    # 0
print(default_dict1['z'])    # 0

# **NOTE as int() returns the default value of integer type, i.e., 0

##### USING LAMBDA #####
default_dict2 = defaultdict(lambda: 0, {'a':10, 'b':20})

print(default_dict2['a'])    # 10
print(default_dict2['b'])    # 20
print(default_dict2['c'])    # 0
print(default_dict2['z'])    # 0


##### USING LAMBDA 2 #####
default_dict3 = defaultdict(lambda: "Key doesn't exists", {'a':'apple', 'b':'ball'})

print(default_dict3['a'])    # apple
print(default_dict3['b'])    # ball
print(default_dict3['c'])    # Key doesn't exists
print(default_dict3['z'])    # Key doesn't exists