Python functions--in formal parameters: *args and **kwargs

Multiple arguments, put in a tuple, with * Start, you can pass multiple parameters, * * is a parameter in accordance with the value of the key to the values of the value of the *args in the dictionary to render the redundant values: (indicates that the arguments in accordance with the location of the value, the more values are given to args, and presented in Ganso Way)

Example:

def foo (x, *args):    Print(x)    print(args) foo (1, 2, 3, 4 , 5) #其中的2, 3,4,5 all to args.

Execution Result:

1(2, 3, 4, 5)

When args is mixed with positional parameters and default parameters: (Note the order of the three)

Example one, (three order is: positional parameter, default parameter, *args)

def foo (x, Y=1, *args):    Print(x)    print(y)     Print (args) foo (1, 2, 3, 4, 5) # where x is the value of 1,y=1 is reset by 2, 3,4,5 has given args

The execution results are:

(3, 4, 5)

Example two, (three order is: position parameter, *args, default parameter)

EF foo (x,*args,y=1):    print(x)    print(args)    Print  (y) foo (1,2,3,4,5)# where x is 1,2,3,4,5 all gives Args,y the default parameter is still 1

The execution results are:

1(2, 3, 4, 5)1

About *, can be viewed from 2 points of view (need to split):

1, from the perspective of formal parameters:

Example:

def foo (*args):# in fact, this action is equivalent to Def foo (a,b,c,d,e):    print(args) foo ( 1,2,3,4,5)# where the 1,2,3,4,5 are passed to the a,b,c,d,e according to the location value respectively

The execution results are:

(1, 2, 3, 4, 5)

2, from the point of view of the actual argument:

Example:

def foo (x, y    , z): Print (x)     Print (y)     Print (z)     foo (* (+))# where * (three-way) is taken apart, Foo (three-way) is passed to X, Y and Z according to the location value.

The execution results are:

123

**kwargs: (indicates that the value of the parameter is presented in a dictionary by the values of the key)

Example:

def foo (x,**Kwargs):    Print(x)    print(Kwargs) foo (1, y=1,a=2,b=3,c=4)# y=1,a=2,b=3,c=4 to the Kwargs in a dictionary

The execution results are:

1(2, 3, 4) {'y'a' a 'b ' ' C ': 4}

Error Example: (due to sequential error)

EF foo (x,**kwargs,*args):    Print(x)    print(args)      Print(Kwargs) foo (1,y=1,a=2,b=3,c=4,2,3,4)

The result of the execution will be an error:

Syntaxerror:invalid syntax

Position parameters, default parameters, **kwargs the order must be positional parameters, default parameters, **kwargs, or will be error:

Example:

def foo (x,y=1,**Kwargs):    Print(x)    print(y)     Print (Kwargs) foo (1,a=2,b=3,c=4) # Send 1 by location to X, y by default parameter is 1,a=2,b=3,c=4 to Kwargs in dictionary mode

The execution results are:

{'a'b'c': 4}

About * *, can be viewed from 2 points of view (need to split):

1, from the perspective of formal parameters:

Example:

def foo (**kwargs):# is actually equivalent to Def foo (y,a,b,c)    print(Kwargs) foo (y=1 , a=2,b=3,c=4)

The execution results are:

{'y'a'a 'b'C  ': 4}

2, from the point of view of the actual argument:

Example one:

deffoo (a,b,c,d):Print(a)Print(b)Print(c)Print(d) Foo (**{"a": 2,"b": 3,"C": 4,"D": 5})#**{"A": 2, "B": 3, "C": 4, "D": 5} is passed to a,b,c,d for each value in the dictionary as a keyword

Execution results are

2345

Example two:

 def  foo (a,b,c,d=1 print   (a)  print  Span style= "COLOR: #000000" > (b)  print   (c) /span>print   (d) Foo ( **{"  a   ": 2,"  b   ": 3, " c  " : 4}) #  **{"a": 2, "B": 3, "C": 4} is passed the value of each value in the dictionary to the A,b,c ; d still follows the default parameter  

The execution results are:

2341

Python functions--in formal parameters: *args and **kwargs