python *args **kwargs-白红宇

python *args **kwargs

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发布时间：2019-06-22

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简单来说，当你传入的参数不能确定是几个的时候会用到＊args和＊＊kwargs，这里星号后边只是个代号，你写成a也可以。

而这两者的区别是如果是键值对就要用后者，反之前者就可以。

同时还可以用（a，＊args，＊＊kwargs）这种方式

具体例子见下面代码：

In [1]: def h(a):   ...:     print a   ...:     In [2]: h(3)3In [3]: def h(*args):   ...:     for i in args:   ...:         print i   ...:         In [4]: h((1, 2, 3))(1, 2, 3)In [5]: a = [1, 2, 3]In [6]: h(a)[1, 2, 3]In [7]: h(3)3In [8]: h(3, 3)33In [9]: h(3, 5)35In [10]: def h(a, *args):   ....:     print a   ....:     for i in args:   ....:         print i   ....:         In [11]: h(3, 4, 5)345In [12]: h(3, a)3[1, 2, 3]In [13]: h(3, (1, 2, 3))3(1, 2, 3)In [14]: h(a)[1, 2, 3]In [15]: h(a, a)[1, 2, 3][1, 2, 3]In [16]: def h(a):   ....:     for i in a:   ....:         print i   ....:         In [17]: h(a)123

In [19]: def h(a, *args):    print 'a', a    for i in args:        print i   ....:         In [20]: h(1, 3, 4)a 134In [21]: h(1, a)a 1[1, 2, 3]In [22]: h(1, (1, (2, 3)))a 1(1, (2, 3))In [23]: h(1, (1, 2, 3))a 1(1, 2, 3)In [24]: h(1, (1, 2, 3), (3, 4))a 1(1, 2, 3)(3, 4)

　注意：此处并没有正确的打印出结果，小括号里的数并没有按行打出，而是直接打出了，正确的用法是要加上＊才可以，见下面的代码

**kwargs的用法：

In [25]: def h(**kwargs):   ....:     for k, v in kwargs.items():   ....:         print k, v   ....:         In [26]: h({'a': 1, 'b': 3})---------------------------------------------------------------------------TypeError                                 Traceback (most recent call last)
     
       in 
      
       ()----> 1 h({'a': 1, 'b': 3})    # 此处没有＊＊，提示错误TypeError: h() takes exactly 0 arguments (1 given)In [27]: h(**{'a': 1, 'b': 3})a 1b 3In [28]: def hh(*args):   ....:     for i in args:   ....:         print i   ....:         In [29]: hh(*(1, 2, 3))   # 此处是正确的使用方法123In [30]: a = (1, 2, 3)In [31]: hh(*a)123In [32]: def hhh(a, *args):   ....:     print a, 'a'   ....:     for i in args:   ....:         print i   ....:         In [33]: hhh(*(1, 3, 4))1 a34

同时使用三种方式的顺序是， def f(a, *args, **kwargs)

In [34]: def hhhh(a, *args, **kwargs):   ....:     print 'a:', a   ....:     for i in args:   ....:         print i   ....:     print 'kwargs:'   ....:     for k, v in kwargs:   ....:         print k, v   ....:         In [35]: hhhh(1, *(2, 3), **{'c': 1, 'b': 3})a: 123kwargs:---------------------------------------------------------------------------ValueError                                Traceback (most recent call last)
     
       in 
      
       ()----> 1 hhhh(1, *(2, 3), **{'c': 1, 'b': 3})
       
         in hhhh(a, *args, **kwargs)      4         print i      5     print 'kwargs:'----> 6     for k, v in kwargs:      7         print k, v      8 ValueError: need more than 1 value to unpackIn [36]: def hhhh(a, *args, **kwargs):    print 'a:', a    for i in args:        print i    print 'kwargs:'    for k, v in kwargs.items:        print k, v   ....:         In [37]: hhhh(1, *(2, 3), **{'c': 1, 'b': 3})a: 123kwargs:---------------------------------------------------------------------------TypeError                                 Traceback (most recent call last)
        
          in 
         
          ()----> 1 hhhh(1, *(2, 3), **{'c': 1, 'b': 3})
          
            in hhhh(a, *args, **kwargs) 4 print i 5 print 'kwargs:'----> 6 for k, v in kwargs.items: 7 print k, v 8 TypeError: 'builtin_function_or_method' object is not iterableIn [38]: def hhhh(a, *args, **kwargs): print 'a:', a for i in args: print i print 'kwargs:' for k, v in kwargs.items(): print k, v ....: In [39]: hhhh(1, *(2, 3), **{'c': 1, 'b': 3})a: 123kwargs:c 1b 3

　注意：items处要加（）

参考见：

https://eastlakeside.gitbooks.io/interpy-zh/content/args_kwargs/When_to_use.html

https://docs.python.org/2/tutorial/controlflow.html#defining-functions

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