Within an application I'm working on. The app is written in multiple layers
such that lower layers provided services to higher layers. Ideally in such an
architecture, the high-level objects know about lower-level ones, but
lower-level objects know nothing about the higher-level ones. There's only one
problem. When this software was originally wirtten, one of the low-level
objects was given knowledge of a higher-level object. This creates a really
ugly dependency that I want to eliminate.
My solution (at least what I'm trying to implement) is a classic one. When a
low-level routine needs info from a higher-level routine, let the higher-level
routine provide a callback which the lower-level routine can call. In this
way, the lower-level routine knows nothing about higher-level routines.
However, Python is complaining about my implementation. It raises an
exception: TypeError: unbound method fn_impl() must be called with X instance
as first argument (got int instance instead)
For simplicity, I've narrowed it down to a bit of sample code. class X is my
low-level service.
class X( object ):
fn = None
@staticmethod
def callX( n ):
return X.fn( n )
Now, the following global stuff represents my higher-level routines:
def fn_impl( n ): # my callback
return n + 1
X.fn = fn_impl # register my callback
Now I can do something which forces my callback (fn_impl) to get called
print X.callX( 3 )
I think I would get '4' printed but instead get the above error. What am I
doing wrong?
Thanks,
Ron--
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