Python装饰器

装饰器：用函数装饰另一个函数或类，让他们提供额外的功能（正常逻辑写在被装饰函数里，其他功能包装在装饰器里[横切功能]，如一些公用功能，以实现与被代理对象业务正交），让你在一个函数的前后去执行代码。它们封装一个函数，并且用这样或者那样的方式来修改它的行为。

def a_new_decorator(a_func):
 
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()")
 
        a_func()
 
        print("I am doing some boring work after executing a_func()")
 
    return wrapTheFunction
 
def a_function_requiring_decoration():
    print("I am the function which needs some decoration to remove my foul smell")
 
a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"
 
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()
 
a_function_requiring_decoration()
#outputs:I am doing some boring work before executing a_func()
#        I am the function which needs some decoration to remove my foul smell
#        I am doing some boring work after executing a_func()

装饰器结构

from functools import wraps

def decorator(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        #其他业务
        result = func(*args, **kwargs) 
        return result
        # 其他业务
    return wrapper 　

# 装饰器自带参数  多嵌套一层
def use_logging(level):
    def decorator(func):
        def wrapper(*args, **kwargs):
            if level == "warn":
                logging.warn("%s is running" % func.__name__)
            elif level == "info":
                logging.info("%s is running" % func.__name__)
            return func(*args)
        return wrapper

    return decorator

@use_logging(level="warn")
def foo(name='foo'):
    print("i am %s" % name)

foo()

用类来写装饰器，类里面有__call__方法的话，函数可以像函数一样调用

from functools import wraps
 
class logit(object):
    def __init__(self, logfile='out.log'):
        self.logfile = logfile
 
    def __call__(self, func):
        @wraps(func)
        def wrapped_function(*args, **kwargs):
            log_string = func.__name__ + " was called"
            print(log_string)
            # 打开logfile并写入
            with open(self.logfile, 'a') as opened_file:
                # 现在将日志打到指定的文件
                opened_file.write(log_string + '\n')
            # 现在，发送一个通知
            self.notify()
            return func(*args, **kwargs)
        return wrapped_function
 
    def notify(self):
        # logit只打日志，不做别的
        pass