*args and **kw in Python

When learning the Python adorner decorator, I encountered *args and **kw two function values passed.

To define functions in Python, you can use general parameters, default parameters, non-keyword parameters, and keyword parameters.

General parameters and default parameters in the previous study we have encountered, and *args and **kw are non-keyword parameters and keyword parameters, the latter are also variable parameters.

A non-keyword parameter is characterized by an asterisk * plus a parameter name, such as *number, which, when defined, can receive any number of parameters and store them in a tuple.

The keyword parameter is characterized by two asterisk * * plus the parameter name, such as **KW, which, when defined, saves any number of parameters received by KW to a dict. The keyword parameter is not necessarily passed in order in the delivery composition (because Key-value within dict is not sequential), but it must be provided as a parameter in the form of pass parameter name = Pass argument value.

Such as:

def try_it (*args, * *kw)     :print'args:', args      print'kw:', kw try_it (1,2,3,4, a=1,b=2,c=3) try_it (  'a', 1, None, a=1, b='2', c=3)

Operation Result:

Args: (1, 2, 3, 4) kw: {'a': 1,'C': 3,'b': 2} args: ('a', 1, None) kw: {'a': 1,'C': 3,'b':'2'}

python中的一般参数、默认参数、非关键字参数和关键字参数可以一起使用，或者只用其中某些，但是请注意，参数定义的顺序必须是：一般参数、默认参数、可变参数和关键字参数，先后顺序不能颠倒。即：

def func (A, B, c=0, *args, **kw):    Pass

Example:

We use the function ' Calculate_sum ', but ' calculate_sum ' requires multiple positional parameters to be passed to ' args ' as tuples. So the function ' ignore_first_calculate_sum ' needs to split the tuple ' Iargs ' and then pass the element as a positional parameter to ' calculate_sum '. Notice that the '*' is used to split the tuple.

So, we call ' Required_sum=calculate_sum (*Iargs) '.

' Required_sum=calculate_sum (Iargs) ' cannot be called because we need to unpack the value before passing it to ' calculate_sum '. Do not use '*' will not unpack the value, you will not be able to perform the desired action.

def calculate_sum (*args):     return  sum (args)def ignore_first_ Calculate_sum (a,*Iargs):     = calculate_sum (*Iargs)     print (" ",required_sum) ignore_first_calculate_sum (12, 1,4,5)  

Reference: CSDN

*args and **kw in Python