［Unpacking Argument Lists］
The reverse situation occurs when the arguments are already in a list or tuple but need to be unpacked for a function call requiring separate positional arguments. For instance, the built-in range()function expects separate start and stop arguments. If they are not available separately, write the function call with the *-operator to unpack the arguments out of a list or tuple:
In the same fashion, dictionaries can deliver keyword arguments with the **-operator:
参考:http://docs.python.org/2.7/tutorial/controlflow.html#unpacking-argument-lists