Answer 1

2nd argument value is default argument. Means if that key not exists in dictionary then it returns default value specified.
So fib.get(4, 0) returns 3 because key 4 exists having value 3.
fib.get(7, 5) returns 5 because key 7 not existing..

dict.get(key) returns error if key not exists...
dict.get(key, default) returns value if key exists, otherwise returns default value...