On Tuesday 19 July 2005 05:09 am, chris wrote: > 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.
Doubtful, Llamas speak Perl. It's some kind of rodent that does Python. "Womp rats", probably. And Pythons, of course. > 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) Well, obviously you have some options, but let's think about everything in that description that *could* be an object: * Data set (1) * Individual row of a data set (1) * Transformation of a data set (2) * Plot data (3) * Plot (3) (probably same as "Plot data" Chances are that "Individual row of a data set" is a dumb enough object to be represented by a built-in type (maybe a tuple). "Data set" is obviously a collection, possibly ordered, so it might subclass "list" (or just be a list). So far, though, you could just use a "list of tuples". Serialization/deserialization of the data is one reason for subclassing list, though. Or you could have an object representing the file or serialized version, which has a method for returning the data set as a list. "Transformation" is almost certainly a class you want to define. This would obviously hold the data required to define the transformation and at least one method for applying the transformation to a data set. You might even define math operators on it so you can use operator notation like: my_transform = Transformation(... initialization values defining the transform ...) xformed_data_set = my_transform * original_data_set But of course, you could just use methods: xformed_data_set = my_transform.apply(original_data_set) "Plot" is another good defined-class. Initialize it with things like the plotting window, scaling, etc and what data set it applies to. It's nice because it can be 1:1 with the actual display widget in your GUI (if you have one). Candidates for attributes would include the lower and upper X and Y limits, log or linear scale, etc. Candidates for methods would be displaying the plot, printing the plot, converting to a string description, etc. > Clearly I'm having some conceptualisation problems here. Hope someone can > shed some light on the subject I think you are trying to use an object as a module. Better to use a module for that. ;-) Meanwhile, meditate on what "object" or "thing" means to you, and how it might map to programming concepts. What is each "thing" that you can imagine swapping out in a more sophisticated implementation with lots of different variations (e.g. data formats, guis, etc). Clearly modularizing along the lines of interchangeable elements is also a good approach. HTH, Terry -- Terry Hancock ( hancock at anansispaceworks.com ) Anansi Spaceworks http://www.anansispaceworks.com -- http://mail.python.org/mailman/listinfo/python-list
