OO design

[Chris Smith]

>>>>> "chris" == chris  <cf_1957 at hotmail.com> writes:

    chris> I have no problem writing bits of functional code to do any
    chris> of the above.  But for the life of me I can't see how I can
    chris> hook them altogether in an OO based framework that I can
    chris> build and extend (with more data formats, manipulations,
    chris> GUI etc).

Chris,
I echo your sentiment. 
My little pet project has recently grown to include a bit of an object
hierarchy.  I've always felt that the Java-esque byzantine pedigree
for everything last class a trifle over-done.
What I used to trigger factorization was whether or not I needed to
branch based on data type:

if input_data.type == "this":
    do_this()
else:
    do_that()

meant I should factor my code to:

class input_data_base()
    pass

class input_data_this(input_data_base)
    pass

class input_data_that(input_data_base)
    pass


With this, my project has a modest number of sensible inheritance
hierarchies (two) and the code that wouldn't benefit from such retains
its procedural character.
OO is a great organizer, but every paradigm runs afoul of Sturgeons
Law if over-driven.
HTH,
Chris