Question about consistency in python language

[lechequier at gmail.com]

Let's say I define a list of pairs as follows:
>>l = [('d', 3), ('a', 2), ('b', 1)]

Can anyone explain why this does not work?
>>h = {}.update(l)

and instead I have to go:
>>h = {}
>>h.update(l)
to initialize a dictionary with the given list of pairs?

when an analagous operation on strings works fine:
>>s = "".join(["d","o","g"])

Seems inconsistent. 

thanks,
Scott