newbie question

[S.Mohideen]

>>> asd={}
>>> asd={1:2,3:4,4:5}
>>> print asd
{1: 2, 3: 4, 4: 5}

>>> asd.has_key(3)
True
>>> asd.update()
>>> print asd
{1: 2, 3: 4, 4: 5}
>>>

what does asd.update() signifies. What is the use of it. Any comments would 
help to understand it.

Thanks
Mohideen