python 裝飾器的使用詳解

注意事項

何時執(zhí)行裝飾器
函數(shù)裝飾器在導(dǎo)入模塊時立即執(zhí)行，而被裝飾的函數(shù)只在明確調(diào)用時運行霉囚。這突出了 Python 程序員所說的導(dǎo)入時和運行時之間的區(qū)別捕仔。
Python何時執(zhí)行裝飾器 - 頑強的allin - 博客園
裝飾器是可以疊加使用的，那么使用裝飾器以后代碼是什么順序呢
對于Python中的@語法糖，裝飾器的調(diào)用順序與使用 @語法糖聲明的順序相反榜跌。
比如

@decorator1
@decorator2
def f(a,b):
    pass

執(zhí)行順序是
f(3, 4) = decorator1(decorator2(f(3, 4)))

@decorator這個語法相當(dāng)于執(zhí)行func = decorator(func)闪唆，為func函數(shù)裝飾并返回

裝飾函數(shù)

(1)被裝飾器的函數(shù)帶有形參

# -*- coding:utf-8 -*-
from enum import Enum, unique
import time

def print_run_time(fun):
    def wrapper(*args, **kwargs):
        print('args:', args)
        print('kwargs:', kwargs)
        start_time = time.time()
        fun(*args, **kwargs)
        run_time = time.time() - start_time
        print('run_time is:', run_time)
    return wrapper

@print_run_time
def test_fun(min_value, max_value):
    sum = 0
    for i in range(min_value, max_value, 1):
        sum += i
    print('sum is:', sum)

wrapper(*args, **kwargs)用來處理被裝飾的函數(shù)帶有各種形參的情況。

當(dāng)調(diào)用

if __name__ == '__main__':
    test_fun(1, 1000000)

輸出

('args:', (1, 1000000))
('kwargs:', {})
('sum is:', 499999500000L)
('run_time is:', 0.07899999618530273)

當(dāng)調(diào)用

if __name__ == '__main__':
    test_fun(min_value=1, max_value=1000000)

輸出

('args:', ())
('kwargs:', {'max_value': 1000000, 'min_value': 1})
('sum is:', 499999500000L)
('run_time is:', 0.08299994468688965)

（2）被裝飾器的函數(shù)帶有返回值

def print_run_time(fun):
    def wrapper(*args, **kwargs):
        print('args:', args)
        print('kwargs:', kwargs)
        start_time = time.time()
        result = fun(*args, **kwargs)
        run_time = time.time() - start_time
        print('run_time is:', run_time)
        return result
    return wrapper

@print_run_time
def test_fun(min_value, max_value):
    sum = 0
    for i in range(min_value, max_value, 1):
        sum += i
    print('sum is:', sum)
    return sum

if __name__ == '__main__':
    result = test_fun(min_value=1, max_value=1000000)
    print('result:', result)

（3）裝飾器帶有形參
帶有參數(shù)的裝飾器需要再增加一層封裝

def print_run_time(debug_flag):
    def fun_wrapper(fun):
        def wrapper(*args, **kwargs):
            start_time = time.time()
            result = fun(*args, **kwargs)
            run_time = time.time() - start_time
            if debug_flag:
                print('args:', args)
                print('kwargs:', kwargs)
                print('run_time is:', run_time)
            return result
        return wrapper
    return fun_wrapper

DEBUG_FLAG = True
@print_run_time(DEBUG_FLAG)
def test_fun(min_value, max_value):
    sum = 0
    for i in range(min_value, max_value, 1):
        sum += i
    print('sum is:', sum)
    return sum

例子中想要給裝飾器添加參數(shù)钓葫，需要再增加一層封裝悄蕾。比如這里做一個輸出開關(guān)。當(dāng)DEBUG_FLAG = True才輸出信息础浮。

（4）@wraps(func)的作用
Python裝飾器（decorator）在實現(xiàn)的時候帆调，被裝飾后的函數(shù)其實已經(jīng)是另外一個函數(shù)了（函數(shù)名等函數(shù)屬性會發(fā)生改變），為了不影響豆同，Python的functools包中提供了一個叫wraps的decorator來消除這樣的副作用番刊。寫一個decorator的時候，最好在實現(xiàn)之前加上functools的wrap诱告，它能保留原有函數(shù)的名稱撵枢。

不加wrap

if __name__ == '__main__':
    result = test_fun(min_value=1, max_value=1000000)
    print('fun_name', test_fun.__name__)

輸出

('fun_name', 'wrapper')

添加wrap

from functools import wraps

def print_run_time(debug_flag):
    def fun_wrapper(fun):
        @wraps(fun)
        def wrapper(*args, **kwargs):
            start_time = time.time()
            result = fun(*args, **kwargs)
            run_time = time.time() - start_time
            if debug_flag:
                print('args:', args)
                print('kwargs:', kwargs)
                print('run_time is:', run_time)
            return result
        return wrapper
    return fun_wrapper

輸出結(jié)果：

('fun_name', 'test_fun')

裝飾類民晒，或者裝飾類中的方法

# -*- coding:utf-8 -*-
from enum import Enum, unique
import time
from functools import wraps
SKILL_MAP = {}
DEBUG_FLAG = True

def register_skill(skill_type):
    def wrapper(cls):
        global SKILL_MAP
        assert cls.skill_cd > 0, 'skill_cd: %s should > 0' % (cls.skill_cd,)
        SKILL_MAP[skill_type] = cls
        return cls
    return wrapper


def print_run_time(debug_flag):
    def fun_wrapper(fun):
        @wraps(fun)
        def wrapper(*args, **kwargs):
            start_time = time.time()
            result = fun(*args, **kwargs)
            run_time = time.time() - start_time
            if debug_flag:
                print('args:', args)
                print('kwargs:', kwargs)
                print('run_time is:', run_time)
            return result
        return wrapper
    return fun_wrapper

@unique
class SkillType(Enum):
    BUFF = 1
    FLY = 2


class BaseSkill(object):
    skill_cd = 0

    @print_run_time(DEBUG_FLAG)
    def create_skill(self):
        pass

    def destroy_skill(self):
        pass


@register_skill(SkillType.BUFF)
class BuffSkill(BaseSkill):
    skill_cd = 1.0

    def create_skill(self):
        super(BuffSkill, self).create_skill()
        print('create buff skill')

    def destroy_skill(self):
        print('destroy buff skill')


@register_skill(SkillType.FLY)
class FlySkill(BaseSkill):
    skill_cd = 2.0

    def create_skill(self):
        super(FlySkill, self).create_skill()
        print('create fly skill')

    def destroy_skill(self):
        super(FlySkill, self).destroy_skill()
        print('destroy fly skill')

def skill_facory(skill_type):
    skill_class = SKILL_MAP[skill_type]
    skill = skill_class()
    return skill

if __name__ == '__main__':
    skill = skill_facory(SkillType.FLY)
    skill.create_skill()
    skill.destroy_skill()