装饰器总结

1.字典推导式实现从字典中提取子集

    prices={'ACME':45,'Apple':320,'IBM':654,'HP':20}
    # >200
    gt200={key:value for key,value in prices.items() if value > 200}
    print(gt200)
    print('------------------------------')
    #key to value
    tech={'Apple','IBM','HP'}
    techDict={key:value for key,value in prices.items() if key in tech}
    print(techDict)

out:

    {'Apple': 320, 'IBM': 654}
    ------------------------------
    {'HP': 20, 'Apple': 320, 'IBM': 654}

2.装饰器decorator

    def deco(func):
        print('before,hello')
        func()
        print('after,hello')
        return func

    def myfunc():
        print('hello~')

    myfunc=deco(myfunc) #等价于@deco(语法糖)
    myfunc()
    myfunc()

output:

    before,hello
    hello~
    after,hello
    hello~   #原函数多调用
    hello~   #第二次没有调用deco()

装饰函数只调用了一次,而且原函数多调用一次
使用内嵌包装函数确保每次装饰函数都被调用

    def deco(func): 
        def _deco():
            print('before,hello')
            func()
            print('after,hello')
        return _deco
    @deco
    def myfunc():
        print('hello~')

    myfunc()
    myfunc()

对带参数的函数进行装饰

    def deco(func):
        def _deco(a,b):#参数不确定:*args,**kwargs
            print('before')
            ret = func(a,b)
            print('after')
            return ret
        return _deco
    @deco
    def myfunc(a,b):
        print(' myfunc(%s,%s) called.'%(a,b))
        return a+b
    myfunc(1,2)

让装饰器带类参数

    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()

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

    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

    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))