Question

我正在尝试在我的应用中实现一个简单的日志记录功能。

class messages(object):

    # Implement decorator here
    def on(self):
        def wrapper():
            # Do something here
        return wrapper

    def off(self):
        def wrapper():
            # Do something here
        return wrapper


class website(object):

    @messages.on #This line can be switched on/off
    def login(self):
        # Do a whole bunch of stuff here
        self.response = "[+] Login Succeeded!"

website = website()
website.login() # prints self.response based on @messages.on/off

但我不确定我需要在装饰师身上申请什么。我尝试过创建实例并添加参数但主要是接收TypeError。我对装饰者来说相当新鲜。任何帮助将不胜感激，我希望下次能记住这一点。

Answer 1

如果您只想让狗吠（如示例所示），则无需启用装饰器
```
this
```

如果要为类中的某些函数启用日志记录，可以使用以下代码执行此操作的代码

class Dog(object):
    def __init__(self):
        self.sound = "Woof!"

    def bark(self):
        return self.sound

示例：

from functools import wraps

class Utilities(object):

    @staticmethod  # no default first argument in logger function
    def logger(f):  # accepts a function
        @wraps(f)  # good practice https://docs.python.org/2/library/functools.html#functools.wraps
        def wrapper(self, *args, **kwargs):  # explicit self, which means this decorator better be used inside classes only
            print("Before:", self.sound)
            result = f(self, *args, **kwargs)
            print("After:", self.sound)
            return result
        return wrapper


class Dog(object):
    def __init__(self):
        self.sound = "Woof!"

    @Utilities.logger
    def run(self):
        """Perform running movement"""
        print("Running")

虽然毕竟不需要在>>> dog = Dog() >>> dog.run() Before: Woof! Running After: Woof!类中存储装饰器功能 - 但最好有一个名为Utilities的单独模块（文件）并将装饰器作为独立函数放在那里

Answer 2

以下是您可以使用的示例装饰器：

class Utilities:

    @staticmethod
    def add_logger(func):
        def wrapped_func(*args, **kwargs):
            # Sample logic, feel free to update this
            try:
                func_response = func(*args, **kwargs)
            except:
                print 'I am error handled by logger'
                func_response = None
            return func_response
        return wrapped_func

让我们现在定义你的课程：

class Dog(object):

    @Utilities.add_logger 
    def bark(self):
        print 'In bark'

    @Utilities.add_logger 
    def my_error_function(self):
        print 'In my_error_function'
        raise Exception  # <--- Raises Exception

现在，我们来看看它的工作原理：

>>> dog = Dog()
>>> dog.bark()
In bark
>>> dog.my_error_function()
In my_error_function
I am error handled by logger  # Content from logger in case of exception

注意： 您不应该在这里创建class存储实用程序功能。创建一个单独的实用程序文件并在那里编写这些函数。

没有上课，你的装饰师应该是（让我们说 utility.py ）：

def add_logger(func):
    def wrapped_func(*args, **kwargs):
        # Sample logic, feel free to update this
        try:
            func_response = func(*args, **kwargs)
        except:
            print 'I am error handled by logger'
            func_response = None
        return func_response
    return wrapped_func

使用它，只需：

import utility

class Dog(object):

    @utility.add_logger
    def bark(self):
        print 'In bark'

在类中使用装饰器

2 个答案: