python函数中形参中的*、**以及实参中的*、**

函数中形参中的*、**以及实参中的*、**"/>

python函数中形参中的*、**以及实参中的*、**

参考

• More Control Flow Tools
• What does ** (double star/asterisk) and * (star/asterisk) do for parameters?

函数定义中

在函数定义中，我们可以在参数前加*，或者加**，其中加*代表接受一个像list或者tuple类型的参数，加**代表接受一个像dict一样的参数。

• 参数有*

def fun(name, *tuple):print("name is ", name)for i in tuple:print("tuple has ", i)fun("pan", 1, 3, 'dong')

结果为：

name is  pan
tuple has  1
tuple has  3
tuple has  dong

a = (1, 2, "dong")
fun("pan", a)

结果为：

name is  pan
tuple has  (1, 2, 'dong')

可以看到，当真正传入一个tuple或者list，并不会一次输出其中的元素，而是将这整个tuple或者list看做一个元素输出。

• 参数有**

def fun(name, **dict):print("name is ", name)for key in dict:print("dict key is", key, end='，')print("value is", dict[key])fun("pan", country="china", city="rizhao")

结果：

name is  pan
dict key is country，value is china
dict key is city，value is rizhao

可以看到，将传入的china和rizhao看做了字典的两个值，country和city看做字典的键。

dic = {"country": "china", "city": "rizhao"}
fun("pan", dic)

报错：

fun() takes 1 positional argument but 2 were given

• 参数有*和**
  参数如果有*和**，那么*要在前面。

def fun(name, *tuple, **dict):print("name is ", name)for i in tuple:print("tuple has ", i)for key in dict:print("dict key is", key, end='，')print("value is", dict[key])fun("pan", 1, 2, 3, country="china", city="rizhao")

结果为：

name is  pan
tuple has  1
tuple has  2
tuple has  3
dict key is country，value is china
dict key is city，value is rizhao

函数调用中

函数定义如下：

def fun(name, country, city, major="cs"):print("name is", name)print("country is", country)print("city is", city)print("major is", major)

fun('pan', 'china', 'rizhao')a = ['pan', 'china', 'rizhao']
fun(*a)a = ('pan', 'china', 'rizhao')
fun(*a)a = {"name": "pan", "city": "rizhao", "country": "china"}
fun(**a)

结果均为：

name is pan
country is china
city is rizhao
major is cs

注意，在使用字典传参数时，字典的键必须和函数的形参名称对应起来。不能有冗余的键，也不能缺少键。

• 冗余

a = {"name": "pan", "city": "rizhao", "country": "china", "temp": 23}
fun(**a)

fun() got an unexpected keyword argument 'temp'

• 缺少

a = {"name": "pan", "city": "rizhao"}
fun(**a)

fun() missing 1 required positional argument: 'country'