[packagekit] yum2 backend

[Owen Taylor]

On Fri, 2008-02-15 at 16:26 +0100, Patryk Zawadzki wrote:
> On Fri, Feb 15, 2008 at 3:58 PM, Robin Norwood <rnorwood at redhat.com> wrote:
> > On Fri, 15 Feb 2008 14:30:53 +0100
> >  Tim Lauridsen <tim.lauridsen at googlemail.com> wrote:
> >
> >  > I spend some time make the yum2 dbus backend work.
> >  >
> >  > Had to comment out all dbus service methods in the base class
> >  > (deamonBackend.py) because it looks like overloading the methods in
> >  > yumDBUSBackend.py was not working, so when calling the methods from
> >
> >  Thanks for fixing that up...I thought it was working for me the other
> >  night, but tests in the harsh light of day show that it doesn't work
> >  for me now either. Any python guys know anything about overloading
> >  decorators, and why this wouldn't be working?
> 
> A decorator is an immediately evaluted function. It is evaluated at
> declaration time, not at instance creation time. If it does some magic
> tricks like passing the decorated method to an external library, it
> does the magic on the exact method that it prepends. Also:
> 
> @foo
> def bar:
>     pass
> 
> is equal to:
> 
> def bar:
>     pass
> bar = foo(bar)
> 
> So you really overload the decorator's output, not the original method.

If you look at dbus.server.method annotation implementation:

 @dbus.service.method(in_signature='i', out_signature='i', ...)
 def bar(self, some_int):
     return int 

Is basically equivalent to:

 def bar(self, some_int):
     return int 
 bar._dbus_in_signature='i'
 bar._dbus_out_signature='i'
 ...

[...] 

So the real question is "how are the _dbus_<blah> properties on the
class's methods being used?".

If we then look at how DBUS-Python implements method lookup, it's by a a
function that is documented as:

def _method_lookup(self, method_name, dbus_interface):
    """Walks the Python MRO of the given class to find the method to invoke.

    Returns two methods, the one to call, and the one it inherits from which
    defines  its D-Bus interface name, signature, and attributes.
    """

So, the fact that the base class method is the one with the properties
should not matter. And I just tried a quick test and it confirmed what I
deduced from the code: it works fine to:

 - Annotate a method in a base class
 - Override in a child class without annotations

So, it's really not clear to me why there would be problems here. 

- Owen

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://lists.freedesktop.org/archives/packagekit/attachments/20080215/b42673d2/attachment-0004.pgp>