python 装饰器详解（python是什么意思）

python 装饰器详解（python是什么意思）

文章目录

​​1 装饰器定义​​​​2 回顾函数（学习装饰器的前提条件）​​

​​2.1 一切皆对象——函数​​​​2.2 函数中定义函数（嵌套函数）​​​​2.3 从函数中返回函数​​​​2.4 将函数作为参数传给另一个函数​​

​​3 第一个装饰器​​​​4 高阶装饰器​​

​​4.1 判断是否调用装饰器​​​​4.2 带参数的装饰器​​

1 装饰器定义

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何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。

2 回顾函数（学习装饰器的前提条件）

2.1 一切皆对象——函数

def hi(name="yasoob"): return "hi " + name print(hi())# output: 'hi yasoob' # 我们甚至可以将一个函数赋值给一个变量，比如greet = hi# 我们这里没有在使用小括号，因为我们并不是在调用hi函数# 而是在将它放在greet变量里头。我们尝试运行下这个 print(greet())# output: 'hi yasoob' # 如果我们删掉旧的hi函数，看看会发生什么！del hiprint(hi())#outputs: NameError print(greet())#outputs: 'hi yasoob'

2.2 函数中定义函数（嵌套函数）

def hi(name="yasoob"): print("now you are inside the hi() function") def greet(): return "now you are in the greet() function" def welcome(): return "now you are in the welcome() function" print(greet()) print(welcome()) print("now you are back in the hi() function") hi()#output:now you are inside the hi() function# now you are in the greet() function# now you are in the welcome() function# now you are back in the hi() function # 上面展示了无论何时你调用hi(), greet()和welcome()将会同时被调用。# 然后greet()和welcome()函数在hi()函数之外是不能访问的，比如： greet()#outputs: NameError: name 'greet' is not defined

2.3 从函数中返回函数

def hi(name="yasoob"): def greet(): return "now you are in the greet() function" def welcome(): return "now you are in the welcome() function" if name == "yasoob": return greet else: return welcome a = hi()print(a)#outputs: #上面清晰地展示了`a`现在指向到hi()函数中的greet()函数#现在试试这个 print(a())#outputs: now you are in the greet() functionhi()()#outputs: now you are in the greet() function

在 ​​if/else​​​ 语句中我们返回 ​​greet​​​ 和 ​​welcome​​​，而不是 ​​greet()​​​ 和 ​​welcome()​​​。为什么那样？这是因为当你把一对小括号放在后面，这个函数就会执行；然而如果你不放括号在它后面，那它可以被到处传递，并且可以赋值给别的变量而不去执行它。 当我们写下 ​​​a = hi()​​​，hi() 会被执行，而由于 name 参数默认是 yasoob，所以函数 greet 被返回了。如果我们把语句改为 a = hi(name = “ali”)，那么 welcome 函数将被返回。我们还可以打印出 ​​hi()()​​，这会输出 now you are in the greet() function。

2.4 将函数作为参数传给另一个函数

def hi(): return "hi yasoob!" def doSomethingBeforeHi(func): print("I am doing some boring work before executing hi()") print(func()) doSomethingBeforeHi(hi)#outputs:I am doing some boring work before executing hi()# hi yasoob!

3 第一个装饰器

（过去写法）即原型，Python Version < 2.4，2004年以前

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()

（现在写法）后面版本的Python中支持了​​@语法糖​​

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 @a_new_decoratordef 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 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()

运行如下代码会存在一个问题：

print(a_function_requiring_decoration.__name__)# Output: wrapTheFunction

这并不是我们想要的！Ouput输出应该是"a_function_requiring_decoration"。这里的函数被​​warpTheFunction​​​替代了。它重写了我们函数的名字和注释文档(docstring)。幸运的是Python提供给我们一个简单的函数来解决这个问题，那就是​​functools.wraps​​。我们修改上一个例子来使用functools.wraps：

from functools import wraps def a_new_decorator(a_func): @wraps(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 @a_new_decoratordef a_function_requiring_decoration(): """Hey yo! Decorate me!""" print("I am the function which needs some decoration to " "remove my foul smell") print(a_function_requiring_decoration.__name__)# Output: a_function_requiring_decoration

4 高阶装饰器

4.1 判断是否调用装饰器

from functools import wrapsdef decorator_name(f): @wraps(f) def decorated(*args, **kwargs): if not can_run: return "Function will not run" return f(*args, **kwargs) return decorated @decorator_namedef func(): return("Function is running") can_run = Trueprint(func())# Output: Function is running can_run = Falseprint(func())# Output: Function will not run

4.2 带参数的装饰器

打出log信息，而且还需指定log的级别

def logging(level): def wrapper(func): def inner_wrapper(*args, **kwargs): print "[{level}]: enter function {func}()".format( level=level, func=func.__name__) return func(*args, **kwargs) return inner_wrapper return wrapper@logging(level='INFO')def say(something): print "say {}!".format(something)# 如果没有使用@语法，等同于# say = logging(level='INFO')(say)@logging(level='DEBUG')def do(something): print "do {}...".format(something)if __name__ == '__main__': say('hello') do("my work")

参考链接：​​https://runoob.com/w3cnote/python-func-decorators.html​​

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