I'd appreciate some experience from the gurus out there to help me understand how to implement MVC design in python code.
Entry number 5 on the wxpython wiki at http://wiki.wxpython.org/index.cgi/BuildingControls discusses MVC design in building reusable controls. The author (Terrel Shumway) suggests that instead of: quote: class MyCoolListControl(...): def __init__(self,parent,id,choices): ... def InsertItem(...): def AppendItem(...): where choices is a static list, do something like this class ListDataModel: """ a minimal model interface to be used by MyCoolListControl """ def __len__(self): """ return the number of items in the list """ def __getitem__(self,index): """ return the specified item """ # consider notifications for observers (e.g. the list control) # allow the user to define whatever mutators are appropriate class MyCoolListControl(...): def __init__(self,parent,id,model): ... def [GS]etModel(self,model): ... This allows the user (programmer) to store the data the way he thinks is best, rather than having to copy the data into your structure whenever it changes. It also reduces the need for kludges like [GS]etItemData for maintaining association of the real data with its currently displayed string representation. endquote The author refers to mvctree.py in wxPython as an example of MVC design. However I'm still too green so I find that particular example too complex and I'm not understanding the separation the author is recommending. Can anyone explain to me further the simple example above and/or supply a simple example of their own? At some level I feel like there's a benefit but I'm failing to grasp it, and how to implement it. If I understand correctly then in the future for example I could completely change how data is stored in the class ListDataModel and not require a change in class MyCoolListControl. Say, hypothetically, I wanted to implement ListDataModel using a dictionary rather than, more naturally, a list, where the "list" data structure is implemented as a dictionary and the list entries correspond to dictionary keys (dictionary values are not used in this case). Then if I understand the MVC concept, class MyCoolListControl need not change at all. If that's true then that's really cool. But I don't get how that works. I think I need a little further expansion of the example or an alternative (20-30 liner) that I can work through. The question arises in the context of wanting to build a dialog with a tree control that presents projects and studys as a tree and allows selection of projects and studies as required by the user. I want to parse a file with contents as follows: BEGIN PROJECT "mpi6_0" STUDY "Cyc0302_0" cyc0302_beanoz_x1.sdy STUDY "Cyc0305_0" cyc0305_beanoz_x1.sdy STUDY "Cyc0308_0" cyc0308_beanoz_x1.sdy STUDY "Cyc0311_0" cyc0311_beanoz_x1.sdy STUDY "Cyc0314_0" cyc0314_beanoz_x1.sdy END PROJECT BEGIN PROJECT "mpi6_1" STUDY "Cyc0302_1" cyc0302_beanoz_x1.sdy STUDY "Cyc0305_1" cyc0305_beanoz_x1.sdy STUDY "Cyc0308_1" cyc0308_beanoz_x1.sdy STUDY "Cyc0311_1" cyc0311_beanoz_x1.sdy STUDY "Cyc0314_1" cyc0314_beanoz_x1.sdy END PROJECT ... I have wriiten a class as follows that extracts the data from the file. import os class ProjectFileDecoder: """ parse project file to obtain project names and associated studies and study files """ def __init__(self, file): self.projects = {} self.parse_file(file) def parse_file(self, file): f = open(file, 'r') dir = os.path.split(file) while 1: line = f.readline() if 'BEGIN PROJECT' in line: proj_name = line.strip().split('"')[1] self.projects[proj_name] = {} elif 'STUDY' in line: study_name = (line.strip().split('"'))[1].strip() study_file = dir[0] + '/' + (line.strip().split('"'))[2].strip() self.projects[proj_name][study_name] = study_file elif not len(line): f.close() break def getProjectNames(self): return self.projects.keys() def getStudyNames(self): return [self.projects[i].keys() for i in self.getProjectNames()] def getStudyFiles(self): return [self.projects[i].values() for i in self.getProjectNames()] At some level this seems to me like the class ListDataModel above. I just need to make a MyTreeControl class. However here GS(et) routines are implemented in the ProjectFileDecoder class (data model?) whereas in the earlier advice they are in class MyCoolListControl. So I'm not understanding how data gets from the DataModel class to the ListControl class. After all the words I've said, I think that's the core misunderstanding I have. Hope someone can help clear that up for me. Chris -- http://mail.python.org/mailman/listinfo/python-list
