Python-装饰器 decorators

菜鸟教程-Python 函数装饰器

1. 在函数中返回函数

def hi(name="tl"):
    def greet():
        return "now you are in the greet() function"
    def welcome():
        return "now you are in the welcome() function"
    if name == "tl":
        return greet
    else:
        return welcome
a = hi()
print(a)
print(a())
# <function hi.<locals>.greet at 0x00000264BDCAA0D0>
# now you are in the greet() function

注意：在返回的时候返回函数名welcome而非welcome()，否则会返回函数的返回值

2. 将函数作为参数传递

def hi():
    return "hi tl"
def doSomeThingBeforeHi(func):
    print("Im in front of Hi!")
    print(func())
doSomeThingBeforeHi(hi)
# Im in front of Hi!
# hi tl

可以看到传递进去了hi()

3. 装饰器

3.1 第一个装饰器

使用装饰器，可以在一个函数的前后执行代码

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_requring_decoration():
    print("I am the function which needs some decoration to remove my foul smell")
a_function_requring_decoration()
a_function_requring_decoration = a_new_decorator(a_function_requring_decoration)
a_function_requring_decoration()
# I am the function which needs some decoration to remove my foul smell
# 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()

3.2 使用’@‘来生成一个装饰器

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_decorator
def a_function_requring_decoration():
    print("I am the function which needs some decoration to remove my foul smell")
a_function_requring_decoration()

@a_new_decorator其实和a_function_requring_decoration = a_new_decorator(a_function_requring_decoration)是相同意思

3.3 装饰器的方法名

按照3.2的方法构建装饰器后，如果我们打印方法名，会出现如下问题：

print(a_function_requring_decoration.__name__)
# wrapTheFunction

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)。我们可以使用functools.wraps解决这一问题

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_decorator
def a_function_requiring_decoration():
    print("I am the function which needs some decoration to "
          "remove my foul smell")
print(a_function_requiring_decoration.__name__)
# a_function_requiring_decoration

3.4 装饰器蓝本规范

from functools import wraps
def decorator_name(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        if not can_run:
            return "Function will not run"
        else:
            return f(*args, **kwargs)
    return decorated
@decorator_name
def func():
    return("Function is running")
can_run = True
print(func())
can_run = False
print(func())

4. 类装饰器

class decorator_class(object):
    def __init__(self, func):
        self._func = func
        print("class decorator initing")
    def __call__(self):
        print("class decorator running")
        self._func()
        print("class decorator ending")
@decorator_class
def func():
    print("function!")
print("----------------------")
func()
# class decorator initing
# ----------------------
# class decorator running
# function!
# class decorator ending