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'