obsidian-sync/日常学习/python/装饰器.md

装饰器的一般语法结构如下：

```python
def decorator(func):  
    def wrapper():  
        # 新增功能或者附加限制条件  
        # ...   
        return func()  
    return wrapper
```

装饰器函数可以不用使用装饰器语法糖@，而是采用原始的方式进行调用。例如，下面是一个用于计算函数运行时间的装饰器函数，它的等效写法是：
```python
import time

def my_decorator(func):
    def wrapper(*args, **kwargs):
        start_time = time.time()
        result = func(*args, **kwargs)
        end_time = time.time()
        print("Function took {:.6f} seconds.".format(end_time - start_time))
        return result
    return wrapper

def my_function(x):
    time.sleep(x)
    return x

decorated_function = my_decorator(my_function)
print(decorated_function(2))
```

装饰器也可以用类进行实现，我们可以定义一个类，将需要被装饰的函数作为一个参数传递给类的构造函数，并重载类的__call__方法。  
例如，下面是一个用于计算函数运行时间的类装饰器，它的等效写法是：
```python
import time

class MyDecorator:
    def __init__(self, func):
        self.func = func
        
    def __call__(self, *args, **kwargs):
        start_time = time.time()
        result = self.func(*args, **kwargs)
        end_time = time.time()
        print("Function took {:.6f} seconds.".format(end_time - start_time))
        return result

@MyDecorator
def my_function(x):
    time.sleep(x)
    return x

print(my_function(2))
```

### 单参数被装饰函数
```python
def my_decorator(func):
    def wrapper(arg):
        print("Calling function...")
        result = func(arg)
        print("Function returned: ", result)
        return result
    return wrapper

@my_decorator
def my_function(x):
    return x * 2

my_function(2)  # 输出：Calling function... Function returned:  4
```

### 多参数被装饰函数
```python
def my_decorator(func):
    def wrapper(*args, **kwargs):
        print("Calling function...")
        result = func(*args, **kwargs)
        print("Function returned: ", result)
        return result
    return wrapper

@my_decorator
def my_function(x, y, z):
    return x + y + z

my_function(2, 3, z=4)  # 输出：Calling function... Function returned:  9
```