Python * args ** kwargs, pythonargskwargs

Python * args ** kwargs, pythonargskwargs

To put it simply, * args and ** kwargs will be used when you cannot determine the number of input parameters. Here, the asterisk is just a code name behind it. You can also write it as.

The difference between the two is that the latter is required for key-value pairs, and the other is true for the former.

You can also use (a, * args, ** kwargs)

 

For specific examples, see the following code:

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)

Note: The result is not correctly printed here. Instead, the number in parentheses is not typed by line, but directly. The correct usage is to add *. See the following code.

** Kwargs usage:

In [25]: def h (** kwargs ):....: for k, v in kwargs. items ():....: print k, v ....: In [26]: h ({'A': 1, 'B': 3}) handle TypeError Traceback (most recent call last) <ipython-input-26-557f772fd853> in <module> () ----> 1 h ({'A': 1, 'B': 3}) # No ** here, error 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) # Here is the correct method of use 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

　

In the same order, 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)<ipython-input-35-6ac13cc71458> in <module>()----> 1 hhhh(1, *(2, 3), **{'c': 1, 'b': 3})<ipython-input-34-18188bbea105> 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)<ipython-input-37-6ac13cc71458> in <module>()----> 1 hhhh(1, *(2, 3), **{'c': 1, 'b': 3})<ipython-input-36-0e0a773cdf48> 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

Note: add () to items ()

 

See:

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

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