Python - 装饰器 - 试图访问方法的父类

Question

这行不通:

def register_method(name=None):
    def decorator(method):
        # The next line assumes the decorated method is bound (which of course it isn't at this point)
        cls = method.im_class
        cls.my_attr = 'FOO BAR'
        def wrapper(*args, **kwargs):
            method(*args, **kwargs)
        return wrapper
    return decorator

装饰器就像电影盗梦空间；您进入的级别越多，它们就越困惑。我正在尝试访问定义方法的类(在定义时)，以便我可以设置该类的属性(或更改属性)。

版本 2 也不起作用:

def register_method(name=None):
    def decorator(method):
        # The next line assumes the decorated method is bound (of course it isn't bound at this point).
        cls = method.__class__  # I don't really understand this.
        cls.my_attr = 'FOO BAR'
        def wrapper(*args, **kwargs):
            method(*args, **kwargs)
        return wrapper
    return decorator

当我已经知道它为什么损坏时，将我损坏的代码放在上面的意义在于它传达了我正在尝试做的事情。

Answer 1

我不认为你可以用装饰器做你想做的事(快速编辑:无论如何，使用方法的装饰器)。构造方法时会调用装饰器，在构造类之前。您的代码无法正常工作的原因是调用装饰器时该类不存在。

jldupont 的评论是要走的路:如果你想设置类的属性，你应该装饰类或使用元类。

编辑:好的，看到您的评论后，我可以想到一个可能适合您的两部分解决方案。使用方法的装饰器设置方法的属性，然后使用元类搜索具有该属性的方法并设置类的适当属性:

def TaggingDecorator(method):
  "Decorate the method with an attribute to let the metaclass know it's there."
  method.my_attr = 'FOO BAR'
  return method # No need for a wrapper, we haven't changed
                # what method actually does; your mileage may vary

class TaggingMetaclass(type):
  "Metaclass to check for tags from TaggingDecorator and add them to the class."
  def __new__(cls, name, bases, dct):
    # Check for tagged members
    has_tag = False
    for member in dct.itervalues():
      if hasattr(member, 'my_attr'):
        has_tag = True
        break
    if has_tag:
      # Set the class attribute
      dct['my_attr'] = 'FOO BAR'
    # Now let 'type' actually allocate the class object and go on with life
    return type.__new__(cls, name, bases, dct)

就是这样。使用如下:

class Foo(object):
  __metaclass__ = TaggingMetaclass
  pass

class Baz(Foo):
  "It's enough for a base class to have the right metaclass"
  @TaggingDecorator
  def Bar(self):
    pass

>> Baz.my_attr
'FOO BAR'

不过，老实说？使用 supported_methods = [...] 方法。元类很酷，但是在您之后必须维护您的代码的人可能会讨厌您。