Do you think Python Dictionary is really Mutable?

Yes, Python Dictionary is mutable. Changing references to keys doesn't lead to the creation of new dictionaries. Rather it updates the current dictionary in place. 

example

a = {'foo': 1, 'bar': 12}
b = a
b['foo'] = 20

print(a)
print(b)

Output

This will give the output −

{'foo': 20, 'bar': 12}
{'foo': 20, 'bar': 12}