Adding multiple keys of the same name to a dict should raise an exception but instead causes a different behavior. For example consider this code,

>>> d = {"x" : "First value", "x" : "Second value", "y" : "Third value"}

One would expect a error because there two keys with the same name or that Python will add "x" : "First value" and will skip "x" : "Second value". But the result is opposite,

>>> d
{'x': 'Second value', 'y': 'Third value'}

Is this a bug or is this an intended behavior? (I may have missed out information related to this in the documentation. Kindly correct me if that's the case.)