d10.py

from collections import defaultdict

#default_factory is mentioned as 'int' class

d=defaultdict(int)
d['a']=1
d['b']=2
#default_factory is given as 'int' class.
print (d)#Output:defaultdict(<class 'int'>, {'a': 1, 'b': 2})


#Returns the default value of int class which is 0.
print (d.__missing__('a')) #Output:0
print (d.__missing__('z'))#Output:0


#__getitem__()   ->If key exists return the value else it will call __missing__() method.
print (d.__getitem__('a'))#Output:0
print (d.__getitem__('z'))#Output:0

#In regular dictionary
d1={'a':1,'b':2}
print (d1)#Output:{'a': 1, 'b': 2}

#__getitem__()   -> If key exists return the value, else returns KeyError.
print (d1.__getitem__('a'))#Output:1
#print (d1.__getitem__('z'))#Output:KeyError: 'z'