Access to static members from inside a method decorator?

glen.coates.bigworld at glen.coates.bigworld at
Wed Oct 4 15:35:45 CEST 2006

I'm developing a library at the moment that involves many classes, some
of which have "exposed" capabilities.  I'm trying to design a nice
interface for both exposing those capabilities, and inspecting
instances to find out what capabilities they have.

At the moment, I'm leaning towards a superclass (Exposed) that defines
a static method which is a decorator (expose) such that any derived
class can mark a method with @Exposed.expose and it will then be later
returned by getExposedMethods(), a la:

class Exposed:
  def expose( f ):

  def getExposedMethods( self ):

class Person( Exposed ):
  def talk( self, ... ):

I'm trying to implement the decorator by having it populate a static
member list of whatever class it's in with a reference to the method.
getExposedMethods() would then return the contents of each of those
lists from itself back to Exposed in the class hierarchy.  The first
problem was that having a reference to the method (i.e. talk()) does
not allow you to get a reference to the enclosing class (I had hoped
im_class would lead me there).  The real hiccup was that explicitly
passing the class as an argument to the decorator generates a undefined
global name error, presumably because at that point of execution the
class object hasn't been fully created/initialised.

So how can this be done?  It doesn't seem like it's possible to pass a
reference to the enclosing class into the decorator, which in turn
means that static tracking of the list of exposed methods is impossible
(at least, if I want to use decorators).

Any ideas that will enable my initial design, or suggestions for an
elegant, workable alternative would be much appreciated.


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