Python - 装饰器 - 试图访问方法的父类

Question

这不起作用:

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

装饰者就像电影Inception; 你去的级别越多,它们就越混乱.我正在尝试访问定义方法的类(在定义时),以便我可以设置类的属性(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

当我已经知道为什么它被破坏时,把我破碎的代码放在上面的重点是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情(快速编辑:使用方法的装饰者,无论如何).构造方法时会调用装饰器,这是在构造类之前.您的代码不起作用的原因是因为调用装饰器时类不存在.

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,看过你的评论后,我可以想到一个可能适合你的两部分解决方案.使用该方法的装饰来设置的属性的方法,然后用一元类搜索与该属性的方法和设置的相应属性类:

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)

而已.使用方法如下:

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'

老实说,但是？使用这种supported_methods = [...]方法.元类很酷,但是那些必须在你之后维护代码的人可能会讨厌你.