裝飾器(decorator)是一種高級(jí)Python語(yǔ)法。裝飾器可以對(duì)一個(gè)函數(shù)、方法或者類進(jìn)行加工。在Python中，我們有多種方法對(duì)函數(shù)和類進(jìn)行加工，比如在Python閉包中，我們見(jiàn)到函數(shù)對(duì)象作為某一個(gè)函數(shù)的返回結(jié)果。相對(duì)于其它方式，裝飾器語(yǔ)法簡(jiǎn)單，代碼可讀性高。因此，裝飾器在Python項(xiàng)目中有廣泛的應(yīng)用。
這是在Python學(xué)習(xí)小組上介紹的內(nèi)容，現(xiàn)學(xué)現(xiàn)賣、多練習(xí)是好的學(xué)習(xí)方式。
第一步：最簡(jiǎn)單的函數(shù)，準(zhǔn)備附加額外功能
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# -*- coding:gbk -*-'''示例1: 最簡(jiǎn)單的函數(shù),表示調(diào)用了兩次'''def myfunc():print("myfunc() called.")myfunc()myfunc() |
第二步：使用裝飾函數(shù)在函數(shù)執(zhí)行前和執(zhí)行后分別附加額外功能
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# -*- coding:gbk -*-'''示例2: 替換函數(shù)(裝飾)裝飾函數(shù)的參數(shù)是被裝飾的函數(shù)對(duì)象，返回原函數(shù)對(duì)象裝飾的實(shí)質(zhì)語(yǔ)句: myfunc = deco(myfunc)'''def deco(func):print("before myfunc() called.")func()print(" after myfunc() called.")return funcdef myfunc():print(" myfunc() called.")myfunc = deco(myfunc)myfunc()myfunc() |
第三步：使用語(yǔ)法糖@來(lái)裝飾函數(shù)
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# -*- coding:gbk -*-'''示例3: 使用語(yǔ)法糖@來(lái)裝飾函數(shù)，相當(dāng)于“myfunc = deco(myfunc)”但發(fā)現(xiàn)新函數(shù)只在第一次被調(diào)用，且原函數(shù)多調(diào)用了一次'''def deco(func):print("before myfunc() called.")func()print(" after myfunc() called.")return func@decodef myfunc():print(" myfunc() called.")myfunc()myfunc() |
第四步：使用內(nèi)嵌包裝函數(shù)來(lái)確保每次新函數(shù)都被調(diào)用
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# -*- coding:gbk -*-'''示例4: 使用內(nèi)嵌包裝函數(shù)來(lái)確保每次新函數(shù)都被調(diào)用，內(nèi)嵌包裝函數(shù)的形參和返回值與原函數(shù)相同，裝飾函數(shù)返回內(nèi)嵌包裝函數(shù)對(duì)象'''def deco(func):def _deco():print("before myfunc() called.")func()print(" after myfunc() called.")# 不需要返回func，實(shí)際上應(yīng)返回原函數(shù)的返回值return _deco@decodef myfunc():print(" myfunc() called.")return 'ok'myfunc()myfunc() |
第五步：對(duì)帶參數(shù)的函數(shù)進(jìn)行裝飾
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# -*- coding:gbk -*-'''示例5: 對(duì)帶參數(shù)的函數(shù)進(jìn)行裝飾，內(nèi)嵌包裝函數(shù)的形參和返回值與原函數(shù)相同，裝飾函數(shù)返回內(nèi)嵌包裝函數(shù)對(duì)象'''def deco(func):def _deco(a, b):print("before myfunc() called.")ret = func(a, b)print(" after myfunc() called. result: %s" % ret)return retreturn _deco@decodef myfunc(a, b):print(" myfunc(%s,%s) called." % (a, b))return a + bmyfunc(1, 2)myfunc(3, 4) |
第六步：對(duì)參數(shù)量不確定的函數(shù)進(jìn)行裝飾
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# -*- coding:gbk -*-'''示例6: 對(duì)參數(shù)數(shù)量不確定的函數(shù)進(jìn)行裝飾，參數(shù)用(*args, **kwargs)，自動(dòng)適應(yīng)變參和命名參數(shù)'''def deco(func):def _deco(*args, **kwargs):print("before %s called." % func.__name__)ret = func(*args, **kwargs)print(" after %s called. result: %s" % (func.__name__, ret))return retreturn _deco@decodef myfunc(a, b):print(" myfunc(%s,%s) called." % (a, b))return a+b@decodef myfunc2(a, b, c):print(" myfunc2(%s,%s,%s) called." % (a, b, c))return a+b+cmyfunc(1, 2)myfunc(3, 4)myfunc2(1, 2, 3)myfunc2(3, 4, 5) |
第七步：讓裝飾器帶參數(shù)
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# -*- coding:gbk -*-'''示例7: 在示例4的基礎(chǔ)上，讓裝飾器帶參數(shù)，和上一示例相比在外層多了一層包裝。裝飾函數(shù)名實(shí)際上應(yīng)更有意義些'''def deco(arg):def _deco(func):def __deco():print("before %s called [%s]." % (func.__name__, arg))func()print(" after %s called [%s]." % (func.__name__, arg))return __decoreturn _deco@deco("mymodule")def myfunc():print(" myfunc() called.")@deco("module2")def myfunc2():print(" myfunc2() called.")myfunc()myfunc2() |
第八步：讓裝飾器帶 類 參數(shù)
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# -*- coding:gbk -*-'''示例8: 裝飾器帶類參數(shù)'''class locker:def __init__(self):print("locker.__init__() should be not called.")@staticmethoddef acquire():print("locker.acquire() called.（這是靜態(tài)方法）")@staticmethoddef release():print(" locker.release() called.（不需要對(duì)象實(shí)例）")def deco(cls):'''cls 必須實(shí)現(xiàn)acquire和release靜態(tài)方法'''def _deco(func):def __deco():print("before %s called [%s]." % (func.__name__, cls))cls.acquire()try:return func()finally:cls.release()return __decoreturn _deco@deco(locker)def myfunc():print(" myfunc() called.")myfunc()myfunc() |
第九步：裝飾器帶類參數(shù)，并分拆公共類到其他py文件中，同時(shí)演示了對(duì)一個(gè)函數(shù)應(yīng)用多個(gè)裝飾器
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# -*- coding:gbk -*-'''mylocker.py: 公共類 for 示例9.py'''class mylocker:def __init__(self):print("mylocker.__init__() called.")@staticmethoddef acquire():print("mylocker.acquire() called.")@staticmethoddef unlock():print(" mylocker.unlock() called.")class lockerex(mylocker):@staticmethoddef acquire():print("lockerex.acquire() called.")@staticmethoddef unlock():print(" lockerex.unlock() called.")def lockhelper(cls):'''cls 必須實(shí)現(xiàn)acquire和release靜態(tài)方法'''def _deco(func):def __deco(*args, **kwargs):print("before %s called." % func.__name__)cls.acquire()try:return func(*args, **kwargs)finally:cls.unlock()return __decoreturn _deco # -*- coding:gbk -*- |
'''示例9: 裝飾器帶類參數(shù)，并分拆公共類到其他py文件中
同時(shí)演示了對(duì)一個(gè)函數(shù)應(yīng)用多個(gè)裝飾器'''
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from mylocker import *class example:@lockhelper(mylocker)def myfunc(self):print(" myfunc() called.")@lockhelper(mylocker)@lockhelper(lockerex)def myfunc2(self, a, b):print(" myfunc2() called.")return a + bif __name__=="__main__":a = example()a.myfunc()print(a.myfunc())print(a.myfunc2(1, 2))print(a.myfunc2(3, 4)) |
以上給大家分享了Python裝飾器入門學(xué)習(xí)教程(九步學(xué)習(xí))，希望對(duì)大家有所幫助。
