typora/note/Python/函数.md

### 函数定义与参数

- def定义

```python
def my_function(fname):
  print(fname + " Gates")

my_function("Bill")
my_function("Steve")
my_function("Elon")
```

- 默认参数

```python
def my_function(country = "China"):
  print("I am from " + country)

my_function()
my_function("Brazil")
```

- 关键字参数：使用key=value形式传递参数，顺序不严格要求

```python
def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Phoebe", child2 = "Jennifer", child3 = "Rory")
```

- 任意参数：相当于多个参数元组

```python
def my_function(*kids):
  print("The youngest child is " + kids[2])

my_function("Phoebe", "Jennifer", "Rory")
```

- pass语句

```python
def myfunction:
  pass
```

### 函数返回值 return

- 返回两个参数，分别接收

```python
>>> def myfunc():
...     return 1,2
... 
>>> a, b = myfunc()
>>> a
1
>>> b
2
>>> 
```

- 返回两个结果，一个变量接收

```python
>>> def myfunc():
...     return 1,2
... 
>>> a= myfunc()
>>> a
(1, 2)
>>> 
```

- 返回值元组形式，多个变量接收，接收变量数超出返回值数量会报错

```python
>>> def myfunc():
...     return (1,2)
... 
>>> a, b = myfunc()
>>> a
1
>>> b
2
>>> a, b, c = myfunc()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: not enough values to unpack (expected 3, got 2)
>>> 
```