Summary of the usage of * args and * * kwargs in Python

sxxbxh 2020-11-16 14:33:40
summary usage args kwargs python


For the most part Python beginners ,*args and **kwargs These two magic variables take a lot of time to explain . So what are they ? When to use them ? We need to figure out these problems , First of all, you need to understand , Actually, it doesn't have to be written as *args and **kwargs. It's just in front of the variable *( asterisk ) Is a must . Let's take a look at Python in *args and **kwargs Let's summarize the usage of .

1、*args Usage of

*args and **kwargs Mainly used for function definition . You can pass an indefinite number of arguments to a function . Indefinite here means that you don't know in advance how many parameters the user will pass to you , So use these two keywords in this scenario .*args Is used to send a variable number of arguments of a non key value pair to a function . Here's an example to help you understand this concept :

def test_ var_ args(f_ _arg, *argv) :

print ("first normal arg:", f_ arg)

for arg in argv :

print ( " another arg through *argv:", arg)

test_ var_ args(' yasoob',' python',' eggs' ,' test' )

This produces the following output :

first normal arg: yasoob

another arg through *argv: python

another arg through *argv: eggs

another arg through *argv : test

2、**kwargs Usage of

**kwargs Allows you to set variable length key value pairs , Pass as an argument to a function . If you want to handle named arguments in a function , You should use **kwargs. Here's an example to get you started :

def greet_ me (**kwargs) :

for key, value in kwargs. items () :

print("{0} == {1}". format (key, value) )

>>> greet me (name="yasoob")

name == yasoob

Now you can see how we're in a function , Processed a key value pair parameter . This is it. **kwargs The basis of , And you can see how effective it is .

3、 Use *args and **kwargs To call a function

Suppose you have such a small function :

def test_ _args_ kwargs (arg1, arg2, arg3) :

print ("arg1:",arg1)

print("arg2:", arg2) .

print ("arg3:",arg3)

You can use *args or ** kwargs To pass parameters to this small function . Here's how to do it :

# Mouth first makes mouth *args .

>>> args = ("two", 3, 5)

>>> test_ args_ kwargs (*args)

arg1: twO

arg2: 3

arg3: 5

# Now let's talk **kwargs:

>>> kwargs = {"arg3": 3, "arg2": "two", "arg1": 5}

>>> test_ args_ kwargs (** kwargs)

arg1: 5

arg2: two

arg3: 3

4、 Standard parameters and *args、**kwargs In the order of use

So if you want to use all three parameters in a function at the same time , This is the order :

some_ func(fargs, *args, **kwargs)

5、 When to use Python in *args and **kwargs?

It really depends on your needs . The most common use case is when writing function decorators . In addition, it can also be used to make monkey patches . Monkey patch means when the program is running ,(runtime) Modify some code . For example , You have a class , There's a man in it called get_ info The function of will call a API And return the corresponding data . If we want to test it , You can put API Call to replace with some test data . for example :

import someclass

def get_ info(self, *args) :

return "Test data"

someclass.get_ info = get_ info

That's all Python in *args and **kwargs To sum up the usage of , Have you solved all your doubts ? Xinxiang treatment of infertility how much money :https://news.fh21.com.cn/yldt/zztlyy/ Zhengzhou Tongji Hospital is good :https://yyk.fh21.com.cn/hospital_6369/pj.html Zhengzhou Tongji Infertility Research Institute :https://yyk.fh21.com.cn/hospital_6369/zn.html

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