Python：如何从类装饰器内部访问装饰类的实例？

Question

这是我的意思的一个例子：

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()

我需要装饰实际的班级吗？

Answer 1

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

Answer 2

请注意，在此上下文中使用“self”只是一种约定，方法只是使用第一个参数作为对实例对象的引用：

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

self 参数作为第一个参数传递。您的 MyDecorator 也是一个模拟函数的类。更容易使其成为实际功能。

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()