python的*args是什么意思？

niexining

1. from itertools import izip_longest
   
2. def grouper(n, iterable, fillvalue=None):
   
3.     "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
   
4.     args = [iter(iterable)] * n
   
5.     return izip_longest(fillvalue=fillvalue, *args)
   
6. for i in grouper(3,'ABCEDFG','x'): print i
   
7. 
   

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windows系统python2.7自带文档库函数手册中，有这样一个例子。

请问*args是怎么用的？ izip_longest的参数一般有两个，一个是迭代对象(iterable)，另一个是填充(filvalue)。为什么在这个例子中，参数却是fillvalue和*args。

另外，某天有朋友问: 如何把列表3个3个地分组？     这儿似乎对这个问题提供了一种别样的解答。

cdtits

貌似指明为元组

niexining

1. ('A', 'B', 'C')
   
2. ('E', 'D', 'F')
   
3. ('G', 'x', 'x')

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这是运行结果.


是不是放了3个迭代器进去, 就3个字符3个字符地迭代?

anonymous0502

4.7.4. 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:

>>>
>>> range(3, 6)             # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args)            # call with arguments unpacked from a list
[3, 4, 5]
In the same fashion, dictionaries can deliver keyword arguments with the **-operator:

>>>
>>> def parrot(voltage, state='a stiff', action='voom'):
...     print "-- This parrot wouldn't", action,
...     print "if you put", voltage, "volts through it.",
...     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 !

                           

niexining

回复 4# anonymous0502

这个两个例子很好.   剩下的就是关于迭代器的还太理解.