Python基础知识—装饰器(Decorator)

• 当有很多Function都要做些前置或者后置的工作时，我们可以使用装饰器统一处理

• 写函数时，经常会出现，一个函数调用另一个函数的现象

def inner_fn(name):
    print(name + " say I'm in")

def outer_fn(name):
    inner_fn(name)
    print(name + " say I'm out")

outer_fn("wgt")

wgt say I'm in
wgt say I'm out

• 而且有时，前后都会调用函数处理

def inner_pre_fn(name):
    print(name+"say I'm in_pre")

def inner_post_fn(name):
    print(name+"say I'm in_post")

def outer_fn(name):
    inner_pre_fn(name)
    print(name+"say I'm out")
    inner_post_fn(name)

outer_fn("wgt")

wgt say I'm in_pre
wgt say I'm out
wgt say I'm in_post

• 使用装饰器

def decorator(fn, name):
    print(name + " say I'm in")
    return fn(name)
  
def outer_fn(name):
    print(name + " say I'm out")
    
decorator(outer_fn, "wgt")

wgt say I'm in
wgt say I'm out

通过上述代码可以发现，一个函数是可以当作参数传入另一个函数的。

• 装饰器有一个特别的写法，就是在你想要修饰的函数上面写上@decorate，也就是@+装饰器名字

def decorator(fn):
    def wrapper(name):
    	  print(name + " say I'm in")
        return fn(name)
    return wrapper

@decorator
def outer_fn(name):
    print(name + " say I'm out")
    
outer_fn("wgt")

wgt say I'm in
wgt say I'm out

• 前后都修饰

def decorator(fn):
    def wrapper(name):
    	  print(name + " say I'm in")
        res = fn(name)
        print(name+"say I'm in_post")
        return res
    return wrapper

@decorator
def outer_fn(name):
    print(name + " say I'm out")
    
outer_fn("wgt")

wgt say I'm in
wgt say I'm out
wgtsay I'm in_post

• 当要对很多函数做同样的装饰时，可以使用装饰器来实现

实例：验证一个用户有没有权限使用这个函数：

def authorization(fn):
    def check_and_do(name):
        if name != "wgt":
            print(name + " has no right!")
            return
        res = fn(name)
        return res
    return check_and_do


@authorization
def outer1(name):
    print(name + " outer1")


@authorization
def outer2(name):
    print(name + " outer2")


@authorization
def outer3(name):
    print(name + " outer3")


outer1("wgf")
outer2("qqq")
outer3("wgt")

wgf has no right!
qqq has no right!
wgt outer3

参考：莫烦Python