Python装饰器学习

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# -*- coding:gbk -*-

‘‘‘示例1: 最简单的函数,表示调用了两次‘‘‘

def myfunc():

    print("myfunc() called.")

myfunc()

myfunc()

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# -*- coding:gbk -*-

‘‘‘示例2: 替换函数(装饰)

装饰函数的参数是被装饰的函数对象，返回原函数对象

装饰的实质语句: myfunc = deco(myfunc)‘‘‘

def deco(func):

    print("before myfunc() called.")

    func()

    print("  after myfunc() called.")

    return func

def myfunc():

    print(" myfunc() called.")

myfunc = deco(myfunc)

myfunc()

myfunc()

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# -*- coding:gbk -*-

‘‘‘示例3: 使用语法糖@来装饰函数，相当于“myfunc = deco(myfunc)”

但发现新函数只在第一次被调用，且原函数多调用了一次‘‘‘

def deco(func):

    print("before myfunc() called.")

    func()

    print("  after myfunc() called.")

    return func

@deco

def myfunc():

    print(" myfunc() called.")

myfunc()

myfunc()

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# -*- coding:gbk -*-

‘‘‘示例4: 使用内嵌包装函数来确保每次新函数都被调用，

内嵌包装函数的形参和返回值与原函数相同，装饰函数返回内嵌包装函数对象‘‘‘

def deco(func):

    def _deco():

        print("before myfunc() called.")

        func()

        print("  after myfunc() called.")

        # 不需要返回func，实际上应返回原函数的返回值

    return _deco

@deco

def myfunc():

    print(" myfunc() called.")

    return ‘ok‘

myfunc()

myfunc()

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# -*- coding:gbk -*-

‘‘‘示例5: 对带参数的函数进行装饰，

内嵌包装函数的形参和返回值与原函数相同，装饰函数返回内嵌包装函数对象‘‘‘

def deco(func):

    def _deco(a, b):

        print("before myfunc() called.")

        ret = func(a, b)

        print("  after myfunc() called. result: %s" % ret)

        return ret

    return _deco

@deco

def myfunc(a, b):

    print(" myfunc(%s,%s) called." % (a, b))

    return a + b

myfunc(1, 2)

myfunc(3, 4)

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# -*- coding:gbk -*-

‘‘‘示例6: 对参数数量不确定的函数进行装饰，

参数用(*args, **kwargs)，自动适应变参和命名参数‘‘‘

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 ret

    return _deco

@deco

def myfunc(a, b):

    print(" myfunc(%s,%s) called." % (a, b))

    return a+b

@deco

def myfunc2(a, b, c):

    print(" myfunc2(%s,%s,%s) called." % (a, b, c))

    return a+b+c

myfunc(1, 2)

myfunc(3, 4)

myfunc2(1, 2, 3)

myfunc2(3, 4, 5)

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# -*- coding:gbk -*-

‘‘‘示例7: 在示例4的基础上，让装饰器带参数，

和上一示例相比在外层多了一层包装。

装饰函数名实际上应更有意义些‘‘‘

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 __deco

    return _deco

@deco("mymodule")

def myfunc():

    print(" myfunc() called.")

@deco("module2")

def myfunc2():

    print(" myfunc2() called.")

myfunc()

myfunc2()

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# -*- coding:gbk -*-

‘‘‘示例8: 装饰器带类参数‘‘‘

class locker:

    def __init__(self):

        print("locker.__init__() should be not called.")

    @staticmethod

    def acquire():

        print("locker.acquire() called.（这是静态方法）")

    @staticmethod

    def release():

        print("  locker.release() called.（不需要对象实例）")

def deco(cls):

    ‘‘‘cls 必须实现acquire和release静态方法‘‘‘

    def _deco(func):

        def __deco():

            print("before %s called [%s]." % (func.__name__, cls))

            cls.acquire()

            try:

                return func()

            finally:

                cls.release()

        return __deco

    return _deco

@deco(locker)

def myfunc():

    print(" myfunc() called.")

myfunc()

myfunc()

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# -*- coding:gbk -*-

‘‘‘mylocker.py: 公共类 for 示例9.py‘‘‘

class mylocker:

    def __init__(self):

        print("mylocker.__init__() called.")

    @staticmethod

    def acquire():

        print("mylocker.acquire() called.")

    @staticmethod

    def unlock():

        print("  mylocker.unlock() called.")

class lockerex(mylocker):

    @staticmethod

    def acquire():

        print("lockerex.acquire() called.")

    @staticmethod

    def unlock():

        print("  lockerex.unlock() called.")

def lockhelper(cls):

    ‘‘‘cls 必须实现acquire和release静态方法‘‘‘

    def _deco(func):

        def __deco(*args, **kwargs):

            print("before %s called." % func.__name__)

            cls.acquire()

            try:

                return func(*args, **kwargs)

            finally:

                cls.unlock()

        return __deco

    return _deco

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# -*- coding:gbk -*-

‘‘‘示例9: 装饰器带类参数，并分拆公共类到其他py文件中

同时演示了对一个函数应用多个装饰器‘‘‘

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 + b

if __name__=="__main__":

    a = example()

    a.myfunc()

    print(a.myfunc())

    print(a.myfunc2(1, 2))

    print(a.myfunc2(3, 4))