d15.py

from collections import defaultdict
#default_factory is not mentioned

d=defaultdict()
d['a']=1
d['b']=2
print (d)#Output:defaultdict(None, {'a': 1, 'b': 2})

print (d['a'])#Output:1
# key 'c' doesn't exists in the dictionary,it raises KeyError
print (d['c'])#Output:KeyError: 'c'