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According to the analysis of the use of * args and * * kwargs in python, I believe that many inexperienced people are at a loss about this. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

A brief introduction

* args and * * kwargs are mainly used for function definition. When the number of parameters passed into the function we need to define is uncertain, we can use * args and * * kwargs instead of the uncertain number of parameters. In fact, it does not have to be written as * args and * kwargs. Only the * (asterisk) in front of the variable is necessary. We can write * var and * * vars. Writing as * args and * * kwargs is just a popular naming convention.

Second use

2.1 * args

When the number of parameters of a function is uncertain and there is no need to specify a parameter name, the format of * args is the regular parameter val1 [, val2,val3....]

Def func_arg (farg, * args):

Print "formal arg:", farg

For arg in args:

Print "another arg:", arg

Func_arg (1, "youzan", 'dba')

Output

In [10]: args (1, "youzan", 'dba')

Formal arg: 1

Another arg: youzan

Another arg: dba

2.2 * * kwargs

You can use * * kwargs when the parameters of the function are named and the number is uncertain. The parameter format of * * kwargs is key1=value1, [key2=value2,key3=value3,....], and the function pair * * kwargs is parsed in a dictionary-like way.

Def func_kwargs (farg, * * kwargs):

Print "formal arg:", farg

For key in kwargs:

Print "keyword arg:% s:% s"% (key, kwargs [key])

Output

In [15]: func_kwargs (1, id=1, name='youzan', city='hangzhou')

Formal arg: 1

Keyword arg: city: hangzhou

Keyword arg: id: 1

Keyword arg: name: youzan

* * another function of kwargs is to convert parameters to dictionaries

In [1]: def kw_dict (* * kwargs):

...: return kwargs

...:

In [2]: print kw_dict (axiom 1, 2, 2, 3)

{'averse: 1,' centering: 3, 'baked: 2}

2.3 examples of synthesis

In [3]: def foo (* args, * * kwargs):

...: print 'args =', args

...: print 'kwargs =', kwargs

...: print'-'

...:

In [4]: foo (1, 2, 3, 4)

Args = (1,2,3,4)

Kwargs = {}

-

In [5]: foo (axiom 1, 2, 2, 3)

Args = ()

Kwargs = {'averse: 1,' canals: 3, 'baked: 2}

-

In [6]: foo (1, 2, 3, 4, 1, 2, 3, 4, 3, 3, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 2, 4, 3)

Args = (1,2,3,4)

Kwargs = {'averse: 1,' canals: 3, 'baked: 2}

-

In [7]: foo ('averse, 1, None, axi1, baked 2, cased 3)

Args = ('a', 1, None)

Kwargs = {'averse: 1,' canals: 3, 'baked:' 2'}

-

2.4 order of use

The order in which standard parameters are used with * args and * * kwargs. When we want to use all three parameters in the function at the same time, the order is as follows:

Func (fargs, * args, * * kwargs)

After reading the above, have you mastered the usage analysis methods of * args and * * kwargs in python? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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