Decorating a DBUS method

I'm trying to combine DBUS' asynchronous method calls with Twisted's Deferreds, but I'm encountering trouble in tweaking the usual DBUS service method decorator to do this.

To use the DBUS async callbacks approach, you'd do:

class Service(dbus.service.Object):

    @dbus.service.method(INTERFACE, async_callbacks=('callback', 'errback'))
    def Resources(self, callback, errback):
        callback({'Magic' : 42})

There's a few places where I simply wrap those two methods in a Deferred, so I thought I'd create a decorator to do that for me:

def twisted_dbus(*args, **kargs):
    def decorator(real_func):

        @dbus.service.method(*args, async_callbacks=('callback', 'errback'), **kargs)
        def wrapped_func(callback, errback, *inner_args, **inner_kargs):
            d = defer.Deferred()
            d.addCallbacks(callback, errback)
            return real_func(d, *inner_args, **inner_kargs)

        return wrapped_func

    return decorator

class Service(dbus.service.Object):

    @twisted_dbus(INTERFACE)
    def Resources(self, deferred):
        deferred.callback({'Magic' : 42})

This, however, doesn't work since the method is bound开发者_StackOverflow中文版 and takes the first argument, resulting in this traceback:

$ python service.py 
Traceback (most recent call last):
  File "service.py", line 25, in <module>
    class StatusCache(dbus.service.Object):
  File "service.py", line 32, in StatusCache
    @twisted_dbus(INTERFACE)
  File "service.py", line 15, in decorator
    @dbus.service.method(*args, async_callbacks=('callback', 'errback'), **kargs)
  File "/usr/lib/pymodules/python2.6/dbus/decorators.py", line 165, in decorator
    args.remove(async_callbacks[0])
ValueError: list.remove(x): x not in list

I could add an extra argument to the inner function there, like so:

def twisted_dbus(*args, **kargs):
    def decorator(real_func):

        @dbus.service.method(*args, async_callbacks=('callback', 'errback'), **kargs)
        def wrapped_func(possibly_self, callback, errback, *inner_args, **inner_kargs):
            d = defer.Deferred()
            d.addCallbacks(callback, errback)
            return real_func(possibly_self, d, *inner_args, **inner_kargs)

        return wrapped_func

    return decorator

But that seems... well, dumb. Especially if, for some reason, I want to export a non-bound method.

So is it possible to make this decorator work?

Why is it dumb? You're already assuming you know that the first positional argument (after self) is a Deferred. Why is it more dumb to assume that you know that the real first position argument is self?

If you also want to support free functions, then write another decorator and use that when you know there is no self argument coming.