setdefault() method of dictionary

Getting the value of the input key

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('b')
print(x)
print(my_dict)

Two
{'a': 'One', 'b': 'Two', 'c': 'Three'}

If input key is not available then key is added.

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('d')
print(x)
print(my_dict)

None
{'a': 'One', 'b': 'Two', 'c': 'Three', 'd': None}

Adding new key with value

my_dict={'a':'One','b':'Two','c':'Three'}
x=my_dict.setdefault('d','Four')
print(x)
print(my_dict)

Four
{'a': 'One', 'b': 'Two', 'c': 'Three', 'd': 'Four'}