python3装饰器理解与实战

前言

装饰器本质上是一个Python函数，它可以让其他函数在不需要做任务代码变动的前提下增加额外功能，装饰器的返回值也是一个函数对象。它经常用于有切面需求的场景，比如：插入日志、性能测试、事务处理、缓存、权限校验等场景。装饰器是解决这类问题的绝佳设计，有了装饰器，我们就可以抽离出大量与函数功能本身无关的雷同代码并继续重用。概括的讲，装饰器的作用就是为已经存在的对象添加额外的功能。
常见装饰器：内置装饰器、类装饰器、函数装饰器、带参数的函数装饰器

实战

原始方法使用：

def use_logging(func_name):
    print("[debug] %s is running" %func_name )


def bar():
    use_logging("bar")
    print("i am bar")

def bar2():
    use_logging("bar2")
    print("i am bar2")

bar()
bar2()

输出：

[debug] bar is running
i am bar
[debug] bar2 is running
i am bar2

函数装饰器古老的方式实现：

def use_logging(func):
    # print("[debug] %s is running" %func_name )
    def wrapper(*args, **kwargs):
        print("[debug] %s is running" % func.__name__)
        return func(*args, **kwargs)

    return wrapper()


def bar():
    # use_logging("bar")
    print("i am bar")

def bar2():
    # use_logging("bar2")
    print("i am bar2")

bar = use_logging(bar)
bar2 = use_logging(bar2)

输出：

[debug] bar is running
i am bar
[debug] bar2 is running
i am bar2

这种方式比较麻烦，每次都要是要使用use_logging函数，所以进一步实现

函数装饰器实现：

def use_logging(func):
    # print("[debug] %s is running" %func_name )
    def wrapper(*args, **kwargs):
        print("[debug] %s is running" % func.__name__)
        return func(*args, **kwargs)

    return wrapper()

@use_logging
def bar():
    # use_logging("bar")
    print("i am bar")

@use_logging
def bar2():
    # use_logging("bar2")
    print("i am bar2")

输出：

[debug] bar is running
i am bar
[debug] bar2 is running
i am bar2

可以看到使用了@use_logging代替了bar = use_logging(bar)，但是结果还是不变的。

带参数的函数装饰器：

def use_logging(level = "debug"):
    def decorator(func):
        def wrapper(*args, **kwargs):
            print("[%s] %s is running" % (level, func.__name__))
            return func(*args, **kwargs)

        return wrapper()
    return decorator

@use_logging("info")
def bar():
    # use_logging("bar")
    print("i am bar")

@use_logging("debug")
def bar2():
    # use_logging("bar2")
    print("i am bar2")

类装饰器的使用：

class Foo(object):
    def __init__(self, func):
        self.func = func

    def __call__(self, *args, **kwargs):
        print(" class decorator running")
        self.func()
        print(" class decorator ending")


@Foo
def bar():
    print("i am bar")

bar()

输出：

 class decorator running
i am bar
 class decorator ending

内置装饰器使用：

class Student(object):
    def __init__(self,name,score):
        self.name = name
        self.__score = score

    @property
    def score(self):
        return self.__score

    @score.setter
    def score(self,score):
        if score < 0 or score > 100:
            raise ValueError("invalid score")
        self.__score = score

s = Student("jarvis","100")
s.score = 99

print(s.score)