python中什么是*args和**kwargs？

def foo(*args, **kwargs):
print('args = ', args)
print ('kwargs = ', kwargs)
print('---------------------------------------')

if __name__ == '__main__':
foo(1,2,3,4)
foo(a=1,b=2,c=3)
foo(1,2,3,4, a=1,b=2,c=3)
foo('a', 1, None, a=1, b='2', c=3)

输出结果

args = (1, 2, 3, 4)

kwargs = {}

args = ()

kwargs = {‘a’: 1, ‘b’: 2, ‘c’: 3}

args = (1, 2, 3, 4)

kwargs = {‘a’: 1, ‘b’: 2, ‘c’: 3}

args = (‘a’, 1, None)

kwargs = {‘a’: 1, ‘b’: ‘2’, ‘c’: 3}

这两个是python中的可变参数，*args代表元祖tuple **kwargs代表的是字典dict

并且同时使用*args和**kwargs时，必须*args参数列要在**kwargs前，像foo(a=1, b=’2’, c=3, a’, 1, None, )这样调用的话，会提示语法错误“SyntaxError: non-keyword arg after keyword arg”。