How to use Python's *args and **kwargs-Python Tutorial-php.cn

How to use Python's *args and **kwargs

高洛峰

Release： 2017-03-19 15:05:18

Original

1050 people have browsed it

*args represents any multiple unnamed parameters, which is a tuple; **kwargs represents keyword parameters, which is a dict.

def fun(*args, **kwargs):
    print &#39;args = &#39;, args
    print &#39;kwargs = &#39;, kwargs
    print &#39;###&#39;
if name == &#39;main&#39;:
    foo(1,2,3,4)
    foo(a=1,b=2,c=3)
    foo(1,2,3,4, a=1,b=2,c=3)
    foo(&#39;a&#39;, 1, None, a=1, b=&#39;2&#39;, c=3)

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The output results are as follows:

args =  (1, 2, 3, 4) 
kwargs =  {} 
###
args =  () 
kwargs =  {&#39;a&#39;: 1, &#39;c&#39;: 3, &#39;b&#39;: 2} 
###
args =  (1, 2, 3, 4) 
kwargs =  {&#39;a&#39;: 1, &#39;c&#39;: 3, &#39;b&#39;: 2} 
###
args =  (&#39;a&#39;, 1, None) 
kwargs =  {&#39;a&#39;: 1, &#39;c&#39;: 3, &#39;b&#39;: &#39;2&#39;} 
###

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As you can see, these two are variable parameters in python .

Note: When using *args and **kwargs at the same time, the *args parameter must be listed before **kwargs, like foo(a=1, b='2', c=3, a', 1, None, ) will prompt Syntax error"SyntaxError: non-keyword arg after keyword arg" if called in this way.

def fun2(param1, *args, **kwargs):
    print &#39;param1 = &#39;, param1
    print &#39;args = &#39;, args
    print &#39;kwargs = &#39;, kwargs
    print &#39;###&#39;
fun2(1, 2, 3, 4, a=1,b=2,c=3)

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Output result:

param1 =  1
args =  (2,3,4)
kwargs =  {&#39;a&#39;: 1, &#39;c&#39;: 3, &#39;b&#39;: 2} 
###

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1 is assigned to param1, the remaining 2, 3, and 4 are assigned to *args, and the others are assigned to **kwargs

There is also a very beautiful usage, which is to create a dictionary:

def kw_dict(**kwargs):
    return kwargs
print kw_dict(a=1,b=2,c=3)

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Result:

{&#39;a&#39;:1, &#39;b&#39;:2, &#39;c&#39;:3}

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In fact, there is a dict class in python. Use dict(a=1,b=2,c=3) to create a dictionary.

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