---
title: Args Kwargs
fid: 20240110-110208
tags: args, kwargs, function, function args, function kwargs
---
<!--Args Kwargs-->

# Args and Kwargs
2024-01-10

Examples From: [Python args and kwargs： Demystified – Real Python](https://realpython.com/python-kwargs-and-args/)


这是 [星号解包](#star-operator) 的进一步深入应用：函数传参。

#### Args 变长传参
##### Passing Multiple Arguments to a Function

```python
def my_sum(a, b, c):
    return a + b + c

my_sum(1,2,3)                     #/// call 
```

缺点是参数的数量是严格固定死的。

##### Passing a list to a Function
```python
def my_sum(my_integers):
    result = 0
    for x in my_integers:
        result += x
    return result

list_of_integers = [1, 2, 3]     
print(my_sum(list_of_integers))    #/// call
```

用列表作为入参后，列表可变长，于是变相解决了可变长传参的问题。但它不是真正的可变长传参，只是改变了问题。

##### Passing Multiple Arguments to a Function using `*args`

```python
def my_sum(*args):
    result = 0
    # Iterating over the Python args tuple
    for x in args:
        result += x
    return result

print(my_sum(1, 2, 3))            #/// call function 实现的的是多参数效果
```

注意: args 可以换成其它名字，重点在于 args 前的一个星号起的作用

#### kwargs Variable in Function

**kwargs** (=keyword arguments) 用以实现可变长关键字参数

##### Iterating over the Python kwargs dictionary
```python
def concatenate(**kwargs):
    result = ""
    # Iterating over the Python kwargs dictionary
    for arg in kwargs.values():
        result += arg
    return result

print(concatenate(a="Real", b="Python", c="Is", d="Great", e="!"))
#/// RealPythonIsGreat!
```
注意: 

1. kwargs 可以换成其它名字，重点在于 kwargs 前的两个星号
2. 此时的参数不是字典，而是关键字参数。想想看，其对应的字典参数版本的函数应该怎么写？


##### Iterating over the keys of the Python kwargs dictionary
```python
def concatenate(**kwargs):
    result = ""
    # Iterating over the keys of the Python kwargs dictionary
    for arg in kwargs:
        result += arg
    return result

print(concatenate(a="Real", b="Python", c="Is", d="Great", e="!"))
#/// abcde
```

此例和上例是什么区别？

在传入参数时，a,b,c 都是变量名，但传入后，这些变量名成了同名**字符串**。
#### Ordering Arguments in a Function

the correct order for your parameters is:

1.  Standard arguments
2.  `*args` arguments
3.  `**kwargs` arguments


```python
def my_function(a, b, *args, **kwargs):
    pass
```

#### Unpacking With the Asterisk Operators

##### 能接收多种类型的入参
```python
my_list = [1, 2, 3]
print(my_list)       #/// [1, 2, 3]
print(*my_list)      #/// 1 2 3
```

print() 既能接受 list, 又能接受多参数，比较万能，其实现就会更复杂

##### 复杂的组合
```python
def my_sum(*args):
    result = 0
    for x in args:
        result += x
    return result

list1 = [1, 2, 3]
list2 = [4, 5]
list3 = [6, 7, 8, 9]

print(my_sum(*list1, *list2, *list3))   #// 
```


解释最后一行！