On Wed, Mar 21, 2018 at 2:15 AM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > On Tue, 20 Mar 2018 11:14:13 +0000, Alister via Python-list wrote: > >> but why would a functional programmer be programming an OOP class? > > I read a really good blog post a while back, which I sadly can no longer > find (I had it bookmarked until Firefox ate my bookmarks) that discussed > exactly that question. > > What they came up with is that its really hard to do useful work for > large applications with 100% pure functional programming styles. As you > add functional techniques to your code, you find your code quality > increasing. Things like pure functions with no hidden state and no side > effects can have a massive positive effect on code quality -- up to a > point. > > As you approach closer and closer to 100% pure functional code, you get > fewer improvements and your code gets harder to write and maintain. > > He maintains that the sweet spot is about 80% functional, and 20% OOP.
Yep, I remember that article. Sadly, I can't find it back now either; maybe someone can craft a regular expression to find it? https://xkcd.com/208/ This week I dived into the source code for an application that's built out of 20 Python files in four package directories plus a top-level "app.py" as its entry point. You'd think that that means I can write my own Python script that imports from those packages and calls on the same code, right? Sadly, no; because this app is 100% OOP and 0% functional. (Not to be confused with a *non-functioning* app; it functions perfectly well. It just doesn't follow *functional programming* idioms.) Deep inside the imported modules, a class's __init__ will check command-line arguments to control its behaviour, and in the event of a problem (eg JSON data lacking vital information), will print a failure message and exit the program. Were this class written in a pure functional style, it would use the construction parameters, and raise an exception if something's wrong. It's entirely possible for a class to follow functional programming style, at least partly. (In theory, it should be possible to use a class in a 100% functional style. A class is just a callable function that then happens to return a thing of a type that has the same name as the thing you called, so there's no reason the two styles can't completely overlap.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
