“**”在Python中意味着什么？

可能重复：
**和*为python参数做些什么？
* args和** kwargs是什么意思？

简单的程序：

storyFormat = """                                       
Once upon a time, deep in an ancient jungle,
there lived a {animal}.  This {animal}
liked to eat {food}, but the jungle had
very little {food} to offer.  One day, an
explorer found the {animal} and discovered
it liked {food}.  The explorer took the
{animal} back to {city}, where it could
eat as much {food} as it wanted.  However,
the {animal} became homesick, so the
explorer brought it back to the jungle,
leaving a large supply of {food}.

The End
"""                                                 

def tellStory():                                     
    userPicks = dict()                              
    addPick('animal', userPicks)            
    addPick('food', userPicks)            
    addPick('city', userPicks)            
    story = storyFormat.format(**userPicks)
    print(story)

def addPick(cue, dictionary):
    '''Prompt for a user response using the cue string,
    and place the cue-response pair in the dictionary.
    '''
    prompt = 'Enter an example for ' + cue + ': '
    response = input(prompt).strip() # 3.2 Windows bug fix
    dictionary[cue] = response                                                             

tellStory()                                         
input("Press Enter to end the program.")     

关注这一行：

    story = storyFormat.format(**userPicks)

**是什么意思？ 为什么不通过一个普通的userPicks ？

---

'**'需要一个字典并提取它的内容并将它们作为参数传递给一个函数。 以此功能为例：

def func(a=1, b=2, c=3):
   print a
   print b
   print b

现在通常你可以像这样调用这个函数：

func(1, 2, 3)

但是你也可以用这样的参数来填充一个字典：

params = {'a': 2, 'b': 3, 'c': 4}

现在你可以将它传递给函数：

func(**params)

有时你会在函数定义中看到这种格式：

def func(*args, **kwargs):
   ...

*args提取位置参数和**kwargs提取关键字参数。

---

**意味着kwargs。 这里有一篇很好的文章。
阅读此：http://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/

---

你可以阅读Python教程的这一部分和这篇文章。

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