Home Backend Development Python Tutorial Detailed explanation of Python's *args and **kwargs

Detailed explanation of Python's *args and **kwargs

Nov 07, 2016 am 11:07 AM
python python tutorial

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

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def fun(*args, **kwargs):

    print 'args = ', args

    print 'kwargs = ', kwargs

    print '###'

if __name__ == '__main__':

    foo(1,2,3,4)

    foo(a=1,b=2,c=3)

    foo(1,2,3,4, a=1,b=2,c=3)

    foo('a', 1, None, a=1, b='2', c=3)

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The output result is as follows:

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args =  (1, 2, 3, 4)

kwargs =  {}

###

args =  ()

kwargs =  {'a': 1, 'c': 3, 'b': 2}

###

args =  (1, 2, 3, 4)

kwargs =  {'a': 1, 'c': 3, 'b': 2}

###

args =  ('a', 1, None)

kwargs =  {'a': 1, 'c': 3, 'b': '2'}

###

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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, ) If called in this way, the syntax error "SyntaxError: non-keyword arg after keyword arg" will be prompted.

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def fun2(param1, *args, **kwargs):

    print 'param1 = ', param1

    print 'args = ', args

    print 'kwargs = ', kwargs

    print '###'

fun2(1, 2, 3, 4, a=1,b=2,c=3)

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Output result:

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param1 =  1

args =  (2,3,4)

kwargs =  {'a': 1, 'c': 3, 'b': 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 , is to create a dictionary:

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def kw_dict(**kwargs):

    return kwargs

print kw_dict(a=1,b=2,c=3)

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Result:

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{'a':1, 'b':2, 'c':3}

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

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