python的*args与**kwargs

Posted 2020-10-27 chen狗蛋儿

1. *args 允许将一个非键值对的可变数量的参数列表（元组）传递给一个函数。

>>> def add(*args):
...     return sum(args)
...
>>> add(1,2,3,4)
10
>>> a = (1,2,3,4)
>>> add(a) # 错误，等价于sum(((1,2,3,4),)),即将元组a与0相加
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in add
TypeError: unsupported operand type(s) for +: ‘int‘ and ‘tuple‘
>>> add(*a)
10
>>> sum(((1,2,3,4),))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: ‘int‘ and ‘tuple‘

 

2. **kwargs 允许将一个键值对的可变数量的参数字典传递给一个函数。

>>> def add(**kwargs):
...     return sum(kwargs.values())
...
>>> add(a=1,b=2,c=3)
6

 

综合：

>>> def f(arg,*args,**kwargs):
...     print(arg)
...     print(args)
...     print(kwargs)
...
>>> f(1,*(1,2,3,4),**{"a":1,"b":2,"c":3})
1
(1, 2, 3, 4)
{‘b‘: 2, ‘c‘: 3, ‘a‘: 1}
>>> f(1,1,2,3,4,a=1,b=2,c=3) # 与上面效果一样

 

 

调用时

def func(a,b,c,d):
    print(a,b,c,d)

args = (1,2,3,4)
func(*args)
1,2,3,4

def func(a,b,c,d):
    print(a,b,c,d)

kargs = {‘a‘:1, ‘b‘:2, ‘c‘:3, ‘d‘:4}
func(**kargs)
1,2,3,4