On 23/01/16 09:30, Cameron Simpson wrote: > Alan will take you up on doing purer OO practices in Python.
In pure OO objects should only expose methods and the data attributes should only be there to support the methods. As such, nobody outside the object has any need to know anything about it. And if you have data attributes that no method uses that's a warning that they maybe are in the wrong place! Likewise a class with no methods maybe should just be a dict or tuple? In the real world of course many objects exist primarily as data stores - especially in business type apps. But the principle remains that it's a very suspicious anti-pattern to see code like: anObj = myClass(...) anX = anObj.X anX = someFunc(anX) # alarm bells here anObj.X = anX This strongly suggests that there's a bit of functionality that should be inside myClass as a method going on inside someFunc(). And of course someFunc may be a series of inline statements, it might not be so conveniently evident as a function call. So as a class designer, if a user of your class (who might be yourself!) insists that they need a setX style method or wants public write access to an attribute you've got to ask the question why? There is a strong chance they really need a new method instead. One of the features of OO programming is that large monolithic algorithms/functions often get split into small chunks distributed over several classes. Finally, if you are really concerned about data access control (but you have to consider why, and how big a risk it is really) then don't forget you can define properties in Python, which can be read-only, write-only, or both. (Of course, in Python it's never bulletproof, but it requires deliberate vandalism to subvert it.) -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
