OO design

[chris]

I've been scripting with python for a while now. Basically writing a few
functions and running in the ipython shell. That's been very useful. But the
more I do this the more I see that I'm doing more or less the same thing
over and over again. So its feels like I need to get into class programming
with all its attendant benefits. However my biggest problem is a conceptual
one. I just can't get my head around defining suitable classes, how they
aquire data and communicate with each other. I'm hoping some of you python
lamas out there might be able to share some of your wisdom on the subject.

What I basically do is a lot of the following::

1. get arbitrary numerical data (typically large data sets in columnar
format or even via COM from other packages. I generally have to deal with
one or more sets of X,Y data)
2. manipulate the data (scaling, least squares fitting, means, peaks,
add/subtract one XY set from another etc)
3. plot data (original set, results of manipulation, scatterplot, histograms
etc  - I use matplotlib)
4. export data (print, csv, shelve)

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

When I think about what I should do I end up with a class XY that has a
method for everything I want to do eg.

class XY:
  def read_file
  def scale_data
  def plot_data
  def shelve_data

But somehow that doesn't feel right, especially when I expect the number of
methods will grow and grow, which would make the class very unwieldy.

Even if that was a legitimate option, I don't understand conceptualy how I
would, for example, plot two different XY objects on the same graph or add
them together point by point. How do two different XY objects communicate
and how do you deal with the thing that they must have in common (the plot
screen for example).

Clearly I'm having some conceptualisation problems here. Hope someone can
shed some light on the subject

bwaha.