Unpacking Argument Lists

这是Python里面比较有意思的一点：

在介绍了Arbitrary Argument Lists之后，文档里提到：

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:

 

>>> list(range(3, 6)) # normal call with separate arguments[3, 4, 5]>>> args = [3, 6]>>> list(range(*args)) # call with arguments unpacked from a list[3, 4, 5] 

 

In the same fasion, dictionaries can deliver keyword arguments with the **-operator:

>>> def parrot(voltage, state='a stiff', action='voom'):... print("-- This parrot wouldn't", action, end=' ')... print("if you put", voltage, "volts through it.", end=' ')... print("E's", state, "!")...>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}>>> parrot(**d)-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised ! 

 

还比如说用在format函数中：

>>> '{2}, {1}, {0}'.format(*'abc') # unpacking argument sequence'c, b, a'