Python中*args和**kargs如何使用

对于初学者来说，看到*args和**kargs就头大，到底它们有何用处，怎么使用？本文将和大家一起来扒一扒，希望对大家学习python有所帮助。

1.*args 实质就是将函数传入的参数，存储在元组类型的变量args当中

def fun_var_args(farg, *args):

    print "farg:", farg

    for value in args:

        print "other arg:", value

fun_var_args(1, "two")

运行：

farg: 1
other arg: two

def fun_var_args(farg, *args):

    print "farg:", farg

    for value in args:

        print "other arg:", value

fun_var_args(1, "two",3,4,5)

运行：

farg: 1
other arg: two
other arg: 3
other arg: 4
other arg: 5

2.第二种场景：

def fun_input_list(var1,var2,var3):
    print var1,var2,var3

var_list=["second",3]
fun_input_list(1,*var_list)

运行：

1 second 3

def fun_input_list(var1,var2,var3):
    print var1,var2,var3

var_list=["second",3,4,5]
fun_input_list(1,*var_list)

运行：（注意：运行有错误，故意的）　　

fun_input_list(1,*var_list)
TypeError: fun_input_list() takes exactly 3 arguments (5 given)

threading中使用*args

1.两个传参

# encoding: utf-8
from time import ctime,sleep
import threading

# 定义自己类的功能
class MyThread(threading.Thread):
    def __init__(self, func, args):
        threading.Thread.__init__(self)
        self.func = func
        self.args = args
    #　调用start自动执行的函数
    def run(self):
        self.func(*self.args)
def player(song_file,time):
    for i in range(2):
        print("start player %s . %s"%(song_file,ctime()) )
    sleep(time)

threads = []

t = MyThread(player,('You and me .mp3',7))

threads.append(t)
t.start()
t.join()

运行：

start player You and me .mp3 . Wed Jul 18 23:40:30 2018
start player You and me .mp3 . Wed Jul 18 23:40:30 2018

1.一个传参，注意args的传值('You and me .mp3',)，这里是元祖类型。

# encoding: utf-8
from time import ctime,sleep
import threading

# 定义自己类的功能
class MyThread(threading.Thread):
    def __init__(self, func, args):
        threading.Thread.__init__(self)
        self.func = func
        self.args = args
    #　调用start自动执行的函数
    def run(self):
        self.func(*self.args)
def player(song_file):
    for i in range(2):
        print("start player %s ."%(song_file) )

threads = []
t = MyThread(player,('You and me .mp3',))
threads.append(t)
t.start()
t.join()

运行：

start player You and me .mp3 .
start player You and me .mp3 .

一个或者多个传参

# encoding: utf-8
from time import ctime,sleep
import threading

# 定义自己类的功能
class MyThread1(threading.Thread):

    def __init__(self, func, args):
        threading.Thread.__init__(self)
        self.func = func
        self.args = args

    def run(self):
        self.func(*self.args)

class MyThread2(threading.Thread):

    def __init__(self, func):
        threading.Thread.__init__(self)
        self.func = func

    def run(self):
        self.func()

def player1():
    for i in range(2):
        print"start player."

def player2(song_file):
    for i in range(2):
        print("start player %s ."%(song_file) )

args = 'You and me .mp3'
threads = []
t1 = MyThread2(player1)
threads.append(t1)
t2 = MyThread1(player2,(args,))
threads.append(t2)
print threads
for t in threads:
    t.setDaemon(True)
    t.start()
for t in threads:
    t.join()

运行：

[<MyThread2(Thread-1, initial)>, <MyThread1(Thread-2, initial)>]
start player.
start player.
start player You and me .mp3 .
start player You and me .mp3 .

3.**kargs 实质就是将函数的参数和值，存储在字典类型的kargs变量中

def fun_var_kargs(farg,**kargs):
    print "firsr value %s"% farg
    for key in kargs.keys():
        print key,
        print kargs[key],

fun_var_kargs(1,var1="second",var2=35,var3="third")

运行：注意字典是二分法读取的，所以先var1="second",然后var3="third",最后var2=35

firsr value 1
var1 second var3 third var2 35

注：print key + ":" + kargs[key],这个为什么不能用

def fun_var_kargs(farg,**kargs):
    print "firsr value %s"% farg
    for key in kargs.keys():
        print key + ":" + kargs[key],

fun_var_kargs(1,var1="second",var2=35,var3="third")

运行：

print key + ":" + kargs[key],
TypeError: cannot concatenate 'str' and 'int' objects
firsr value 1
var1:second var3:third

4.**kargs的第二种使用场景

def fun_input_dic(var1,var2,var3):
    print var1,var2,var3

dic_input={"var2":2,"var3":"third"}
fun_input_dic(1,**dic_input)

运行：

1 2 third

注意*dic_input的运行结果，那就跟*dic_input用法一样了。

def fun_input_dic(var1,var2,var3):
    print var1,var2,var3

dic_input={"var2":2,"var3":"third"}
fun_input_dic(1,*dic_input)

运行：

1 var3 var2