Python：如何从类装饰器内部访问被装饰类的实例？

Question

这里有个例子可以说明我的意思：

class MyDecorator(object):    
    def __call__(self, func):
        # At which point would I be able to access the decorated method's parent class's instance?
        # In the below example, I would want to access from here: myinstance
        def wrapper(*args, **kwargs):
            return func(*args, **kwargs)
        return wrapper

class SomeClass(object):
    ##self.name = 'John' #error here
    name="John"

    @MyDecorator()
    def nameprinter(self):
        print(self.name)

myinstance = SomeClass()
myinstance.nameprinter()

我需要给这个类加上装饰器吗？

Answer 1

self这个参数是作为第一个参数传递的。另外，你的MyDecorator其实是一个模拟函数的类。把它直接写成一个真正的函数会更简单。

def MyDecorator(method):
    def wrapper(self, *args, **kwargs):
        print 'Self is', self
        return method(self, *args, **kwargs)
    return wrapper

class SomeClass(object):
    @MyDecorator
    def f(self):
       return 42

print SomeClass().f()

Answer 2

请注意，在这个上下文中，“self”的使用只是一个约定，方法只是把第一个参数当作对实例对象的引用：

class Example:
  def __init__(foo, a):
    foo.a = a
  def method(bar, b):
    print bar.a, b

e = Example('hello')
e.method('world')

Answer 3

class MyDecorator(object):
    def __call__(self, func):
      def wrapper(that, *args, **kwargs):
        ## you can access the "self" of func here through the "that" parameter
        ## and hence do whatever you want        
        return func(that, *args, **kwargs)
      return wrapper

当然可以！请把你想要翻译的内容发给我，我会帮你用简单易懂的语言解释清楚。