Python 学习入门（17）—— args, kwargs

The special syntax, *args and **kwargs in function definitions is used to pass a variable number of arguments to a function. The single asterisk form (*args) is used to pass a non-keyworded, variable-length argument list, and the double asterisk form is used to pass a keyworded, variable-length argument list. Here is an example of how to use the non-keyworded form. This example passes one formal (positional) argument, and two more variable length arguments.

def test_var_args(farg, *args):    print "formal arg:", farg    for arg in args:        print "another arg:", argtest_var_args(1, "two", 3)

Results:

formal arg: 1another arg: twoanother arg: 3

Here is an example of how to use the keyworded form. Again, one formal argument and two keyworded variable arguments are passed.

def test_var_kwargs(farg, **kwargs):    print "formal arg:", farg    for key in kwargs:        print "another keyword arg: %s: %s" % (key, kwargs[key])test_var_kwargs(farg=1, myarg2="two", myarg3=3)

Results:

formal arg: 1another keyword arg: myarg2: twoanother keyword arg: myarg3: 3

Using *args and **kwargs when calling a function

This special syntax can be used, not only in function definitions, but also when calling a function.

def test_var_args_call(arg1, arg2, arg3):    print "arg1:", arg1    print "arg2:", arg2    print "arg3:", arg3args = ("two", 3)test_var_args_call(1, *args)

Results:

arg1: 1arg2: twoarg3: 3

Here is an example using the keyworded form when calling a function:

def test_var_args_call(arg1, arg2, arg3):    print "arg1:", arg1    print "arg2:", arg2    print "arg3:", arg3kwargs = {"arg3": 3, "arg2": "two"}test_var_args_call(1, **kwargs)

Results:

arg1: 1arg2: twoarg3: 3

代码示例

#!/usr/bin/python# -*- coding:utf-8 -*-## http://blog.ithomer.net# *argsdef test1(farg, *args):    print "formal arg", farg    for arg in args:        print "another arg:", arg# **kwargsdef test2(farg, **kwargs):    print "formal arg", farg    for key in kwargs:        print "another keyword arg: %s, %s" % (key, kwargs[key])# *argsdef test3(arg1, arg2, arg3):    print "arg1:", arg1    print "arg2:", arg2    print "arg3:", arg3# **kwargsdef test4(arg1, arg2, arg3):    print "arg1:", arg1    print "arg2:", arg2    print "arg3:", arg3# *argsdef test5(*args):    for count, thing in enumerate(args):        print "%d -> %s" % (count, thing)# **kwargsdef test6(**kwargs):    for name, value in kwargs.items():        print name, "=", valuedef test7(a, b, c):    print "a=",a, "& b=", b, "& c=", cif __name__ == "__main__":    test1(1, "two", 3)    test2(farg=1, myarg2='two', myargs=3)    args = ("two", 3)    test3(1, *args)    kwargs = {"arg3":3, "arg2":"two"}    #test4(1, **kwargs)    test4(arg1=1, **kwargs)    test5("apple", "banana", "cabbage")    test6(apple="fruit", cabbage="vagetable")    mylist = ['aa', 'bb', 'cc']    test7(*mylist)

运行结果：

formal arg 1
another arg: two
another arg: 3
formal arg 1
another keyword arg: myarg2, two
another keyword arg: myargs, 3
arg1: 1
arg2: two
arg3: 3
arg1: 1
arg2: two
arg3: 3
0 -> apple
1 -> banana
2 -> cabbage
cabbage = vagetable
apple = fruit
a= aa & b= bb & c= cc

参考推荐：

How to use *args and **kwargs in Python

python *args and * kwargs