Understanding *args and **kwargs in Python

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Python is the simplest way to support mutable parameters, such as using default parameters, such as:

DefTest_defargs(One,Both= 2): Print  ' Required argument: ' , one print  ' Optional argument: '  Twotest_defargs (1< Span class= "com" ># result:# Required argument:1 # Optional argument:2test_defargs (1, 3) # Result:# Required argument:1# Optional Argument:3                

Of course, the topic in this article is not about default parameters, but another way to achieve variable parameters (Variable Argument): Using *args and **kwargs syntax. Where *args is a mutable list of positional arguments, **kwargs is a variable keyword arguments list. Also, *args must precede **kwargs, because positional arguments must precede keyword arguments.

The basic usage of both is introduced first.

The following example uses *args and contains a required parameter:

DefTest_args(First, *Args): Print ' Required argument: ',Firstfor v in Args: print  ' Optional argument: ' ,< Span class= "PLN" > Vtest_args (1, 2, 3, Span class= "lit" >4) # result: # Required Argument:1# Optional argument:2 # Optional Argument:3# Optional argument:4      /span>                

The following example uses *kwargs and contains a list of required parameters and *args:

DefTest_kwargs(First, *Args, **Kwargs): Print ' Required argument: ',FirstForVInchArgs: Print ' Optional argument (*args): ',VForK,VInchKwargs.Items(): Print ' Optional argument%s (*kwargs):%s ' % (K,V)Test_kwargs(1, 2, 3 , 4, K1 =5, K2= 6) # results: # Required Argument:1# Optional argument (*args): 2# Optional argument (*args): 3# Optional argument (*args): 4 # Optional argument K2 (*kwargs): 6# Optional argument K1 (*kwargs): 5             

The *args and **kwargs grammars can be used not only in function definitions, but also in function calls. The difference is that if you use *args and **kwargs at the location where the function is defined is a process that takes the parameter pack, then it is a procedure to unpack the parameters when the function is called. The following example is used to deepen understanding:

DefTest_args(First,Second,Third,Fourth,Fifth): Print ' First argument: ',FirstPrint ' Second argument: ',SecondPrint ' Third argument: ',ThirdPrint ' Fourth argument: ',FourthPrint ' Fifth argument: ',Fifth# Use *argsArgs= [1, 2, 3, 4, 5]Test_args(*Args)# results:# First Argument:1# Second Argument:2# Third Argument:3# Fourth Argument:4# Fifth Argument:5# Use **kwargsKwargs= { ' First ': 1, ' Second ': 2, ' Third ': 3, : 4,  ' fifth ' : 5}test_args (**kwargs# results:# first argument:1 # Second argument:2# third Argument:3# fourth argument:4# fifth argument:5   

Functions can be easily defined using *args and **kwargs, and extensibility can be enhanced for future code maintenance.

Understanding *args and **kwargs in Python